BUG: pandas.Index takes multidimensional array as input
#### Code Sample, a copy-pastable example if possible

```python
idx = pd.Index(data=[[1, 2], [1, 2], [2, 3]])

# some cases where this causes error:
idx.get_duplicates()
idx.drop_duplicates()

```
#### Problem description

According to the documentation, pandas.Index takes a 1-dimensional array-like data as input, which is clearly violated in the example.

#### Expected Output

Option 1: pandas.Index should throw an error in this case.
Option 2: the documentation of pandas.Index should be updated. In this case, methods of the Index class should be checked, since nor get_duplicates, nor drop_duplicates are prepared for this kind of input.

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

<details>

INSTALLED VERSIONS
------------------
commit: c818a22417c4d43f55b934caa8ba011ba814b9d5
python: 3.6.4.final.0
python-bits: 64
OS: Linux
OS-release: 4.13.0-36-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.23.0.dev0+484.gc818a22
pytest: 3.4.2
pip: 9.0.1
setuptools: 38.5.1
Cython: 0.27.3
numpy: 1.14.1
scipy: 1.0.0
pyarrow: 0.8.0
xarray: 0.10.1
IPython: 6.2.1
sphinx: 1.7.1
patsy: 0.5.0
dateutil: 2.6.1
pytz: 2018.3
blosc: None
bottleneck: 1.2.1
tables: 3.4.2
numexpr: 2.6.4
feather: 0.4.0
matplotlib: 2.2.0
openpyxl: 2.5.0
xlrd: 1.1.0
xlwt: 1.3.0
xlsxwriter: 1.0.2
lxml: 4.1.1
bs4: 4.6.0
html5lib: 1.0.1
sqlalchemy: 1.2.4
pymysql: 0.8.0
psycopg2: None
jinja2: 2.10
s3fs: 0.1.3
fastparquet: 0.1.4
pandas_gbq: None
pandas_datareader: None

</details>
