Error when unpickling subclass of pandas.DataFrame: __getstate__ doesn't return _item_cache and __setstate__ doesn't set self._internal_names before setting self._metadata
#### Code Sample

```python
import pandas as pd
import numpy as np

class TSDF(pd.DataFrame):
    _metadata = ['time_colname', 'ts_value_colname']

    def __init__(self, data, time_colname, index=None, columns=None,
                 dtype=None, copy=True,
                 ts_value_colname=None):

        super(TSDF, self).__init__(data=data, index=None, columns=columns,
                                   dtype=dtype, copy=copy)
        self.time_colname = time_colname
        self.ts_value_colname = ts_value_colname

    @property
    def time_colname(self):
        """
        Time axis column name
        """
        return self.__time_colname

    @time_colname.setter
    def time_colname(self, val):
        if val is None:
            self.__time_colname = val
        else:
            if isinstance(val, str):
                if val not in self.columns and val not in self.index.names:
                    raise('column not in data frame')
                self.__time_colname = val

    @property
    def ts_value_colname(self):
        """
        Column name of target value.
        """
        return self.__ts_value_colname

    @ts_value_colname.setter
    def ts_value_colname(self, val):
        if val is None:
            self.__ts_value_colname = val
        else:
            if isinstance(val, str):
                if val not in self.columns:
                    raise('column not in dataframe')
                if self.shape[0] > 0 and \
                        not all(
                            [isinstance(v, (int, float, np.number)) for v in
                             self[val]]):
                    raise('the ts_value_colname column is not numeirc')
                self.__ts_value_colname = val

    data = {'date': pd.to_datetime(['2017-01-01', '2017-01-02', '2017-01-03',
                                    '2017-01-04', '2017-01-05', '2017-01-06']),
            'actual': [1., 2., 2., 3., 3., 4.]
            }

    tsdf = TSDF(data, time_colname='date', ts_value_colname='actual')
    tsdf.to_pickle('test.pkl')
    tsdf_pkl = pd.read_pickle('test.pkl')
```
#### Problem description
I'm creating a subclass of pandas.DataFrame. I have some complicated attribute setters, because I wanted to enforce certain data structure to avoid error in downstream process. I'm having trouble unpickling objects of my subclass and I think I have identified the cause.
If you could confirm that my understanding below is correct, I'm happy to create a PR for this. 

1)	In the \__setstate\__ method in generic.py, in the following code, ```set(self._internal_names + self._metadata)``` returns an unordered set, which means self._metadata could be set before self._internal_names are set. This becomes problematic when  my attribute setter needs to access the object that’s not fully set yet.  I got "AttributeError: 'TimeSeriesDataFrame' object has no attribute '_data'"
```
# set in the order of internal names
# to avoid definitional recursion
# e.g. say fill_value needing _data to be
# defined
meta = set(self._internal_names + self._metadata)
for k in list(meta):
    if k in state:
        v = state[k]
        object.__setattr__(self, k, v)
```
2)	In the \__getstate\__ method in generic.py, _item_cache is not returned as part of the state, which caused "AttributeError: 'TimeSeriesDataFrame' object has no attribute '_item_cache', when my attribute setter contains some code that need to access _item_cache.
```
def __getstate__(self):
    meta = {k: getattr(self, k, None) for k in self._metadata}
    return dict(_data=self._data, _typ=self._typ,
            _metadata=self._metadata,
            **meta)
```
#### Output of ``pd.show_versions()``

<details>

INSTALLED VERSIONS
------------------
commit: None
python: 3.5.2.final.0
python-bits: 64
OS: Windows
OS-release: 10
machine: AMD64
processor: Intel64 Family 6 Model 61 Stepping 4, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None
LOCALE: None.None
pandas: 0.23.0
pytest: 3.6.1
pip: 10.0.1
setuptools: 39.2.0
Cython: 0.28.3
numpy: 1.14.3
scipy: 1.1.0
pyarrow: None
xarray: None
IPython: 6.4.0
sphinx: None
patsy: 0.5.0
dateutil: 2.7.3
pytz: 2018.4
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: 2.2.2
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: 0.9999999
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: None
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None

</details>
