Cannot `style.background_gradient`  on an `Int64` column
```python
old = pd.Series(range(9))
new = pd.Series(range(9), dtype='Int64')

print(old.min(), old.values.min(), new.min())  # =0 OK
print(new.values.min()) # KO

old.to_frame().style.background_gradient() # OK
new.to_frame().style.background_gradient() # KO
```

#### Problem description

Similarly to https://github.com/pandas-dev/pandas/issues/25580, the newer Int64 backend is missing some basic functionality.

Expected: values.min() is available, gradients are displayed

Actual:
```python
----> 1 print(new.values.min())
AttributeError: 'IntegerArray' object has no attribute 'min'
```
and full stack of the `background_gradient` error:

<details>

```
AttributeError                            Traceback (most recent call last)
~/virtualenvs/jupyter/lib/python3.6/site-packages/IPython/core/formatters.py in __call__(self, obj)
    343             method = get_real_method(obj, self.print_method)
    344             if method is not None:
--> 345                 return method()
    346             return None
    347         else:

~/virtualenvs/jupyter/lib/python3.6/site-packages/pandas/io/formats/style.py in _repr_html_(self)
    161         Hooks into Jupyter notebook rich display system.
    162         """
--> 163         return self.render()
    164 
    165     @Appender(_shared_docs['to_excel'] % dict(

~/virtualenvs/jupyter/lib/python3.6/site-packages/pandas/io/formats/style.py in render(self, **kwargs)
    457         * table_attributes
    458         """
--> 459         self._compute()
    460         # TODO: namespace all the pandas keys
    461         d = self._translate()

~/virtualenvs/jupyter/lib/python3.6/site-packages/pandas/io/formats/style.py in _compute(self)
    527         r = self
    528         for func, args, kwargs in self._todo:
--> 529             r = func(self)(*args, **kwargs)
    530         return r
    531 

~/virtualenvs/jupyter/lib/python3.6/site-packages/pandas/io/formats/style.py in _apply(self, func, axis, subset, **kwargs)
    536         if axis is not None:
    537             result = data.apply(func, axis=axis,
--> 538                                 result_type='expand', **kwargs)
    539             result.columns = data.columns
    540         else:

~/virtualenvs/jupyter/lib/python3.6/site-packages/pandas/core/frame.py in apply(self, func, axis, broadcast, raw, reduce, result_type, args, **kwds)
   6485                          args=args,
   6486                          kwds=kwds)
-> 6487         return op.get_result()
   6488 
   6489     def applymap(self, func):

~/virtualenvs/jupyter/lib/python3.6/site-packages/pandas/core/apply.py in get_result(self)
    149             return self.apply_raw()
    150 
--> 151         return self.apply_standard()
    152 
    153     def apply_empty_result(self):

~/virtualenvs/jupyter/lib/python3.6/site-packages/pandas/core/apply.py in apply_standard(self)
    255 
    256         # compute the result using the series generator
--> 257         self.apply_series_generator()
    258 
    259         # wrap results

~/virtualenvs/jupyter/lib/python3.6/site-packages/pandas/core/apply.py in apply_series_generator(self)
    284             try:
    285                 for i, v in enumerate(series_gen):
--> 286                     results[i] = self.f(v)
    287                     keys.append(v.name)
    288             except Exception as e:

~/virtualenvs/jupyter/lib/python3.6/site-packages/pandas/core/apply.py in f(x)
     76 
     77             def f(x):
---> 78                 return func(x, *args, **kwds)
     79         else:
     80             f = func

~/virtualenvs/jupyter/lib/python3.6/site-packages/pandas/io/formats/style.py in _background_gradient(s, cmap, low, high, text_color_threshold)
    939 
    940         with _mpl(Styler.background_gradient) as (plt, colors):
--> 941             smin = s.values.min()
    942             smax = s.values.max()
    943             rng = smax - smin

AttributeError: ("'IntegerArray' object has no attribute 'min'", 'occurred at index 0')
```

</details>

#### Output of ``pd.show_versions()``

<details>
INSTALLED VERSIONS

commit: None
python: 3.6.8.final.0
python-bits: 64
OS: Linux
OS-release: 3.10.0-1062.1.1.el7.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.24.2
pytest: 5.0.1
pip: 19.2.3
setuptools: 41.0.1
Cython: None
numpy: 1.16.3
scipy: 1.3.0
pyarrow: None
xarray: None
IPython: 7.5.0
sphinx: None
patsy: None
dateutil: 2.8.0
pytz: 2019.1
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: 3.1.0
openpyxl: None
xlrd: 1.2.0
xlwt: None
xlsxwriter: None
lxml.etree: 4.3.3
bs4: None
html5lib: None
sqlalchemy: 1.3.3
pymysql: None
psycopg2: None
jinja2: 2.10.1
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None
gcsfs: None

</details>
