Implement DataFrame.pop

[itholic]

Resolves #788

like pandas.DataFrame.pop (https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.pop.html?highlight=pop#pandas.DataFrame.pop) now we can pop column from koalas DataFrame like below:

>>> import databricks.koalas as ks
>>> import numpy as np
>>>
>>> df = ks.DataFrame([('falcon', 'bird', 389.0),
...                   ('parrot', 'bird', 24.0),
...                   ('lion', 'mammal', 80.5),
...                    ('monkey','mammal', np.nan)],
...                   columns=('name', 'class', 'max_speed'))
>>>
>>> df.pop('class')
0      bird
1      bird
2    mammal
3    mammal
Name: class, dtype: object
>>>
>>> df
     name  max_speed
0  falcon      389.0
1  parrot       24.0
2    lion       80.5
3  monkey        NaN

(use pandas.DataFrame.pop example)

Unlike pandas, we should remove column information via internal frame.

and when we remove column from internal frame, maybe we should remove related metadata also (like _data_columns, _column_index ...).

[codecov-io]

Codecov Report

Merging #791 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff            @@
##           master    #791      +/-   ##
=========================================
+ Coverage    94.3%   94.3%   +<.01%     
=========================================
  Files          32      32              
  Lines        5828    5831       +3     
=========================================
+ Hits         5496    5499       +3     
  Misses        332     332

Impacted Files	Coverage Δ
databricks/koalas/missing/frame.py	100% <ø> (ø)	⬆️
databricks/koalas/frame.py	96.79% <100%> (ø)	⬆️

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[ueshin]

LGTM.

[ueshin]

Thanks! merging.

[itholic]

@ueshin Thanks :)