Enable DataFrame setting value as list of labels. (Resolves #894)

[itholic]

Resolves #894

for below DataFrame,

>>> df = ks.DataFrame([[1, 2], [4, 5], [7, 8]],
...                   index=['cobra', 'viper', 'sidewinder'],
...                   columns=['max_speed', 'shield'])
>>> df
            max_speed  shield
cobra               1       2
viper               4       5
sidewinder          7       8

now we can set value for all items matching the list of labels like Pandas.

>>> df.loc[['viper', 'sidewinder'], ['shield']] = 50
>>> df
            max_speed  shield
cobra               1       2
viper               4      50
sidewinder          7      50

[codecov-io]

Codecov Report

Merging #905 into master will increase coverage by 0.15%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #905      +/-   ##
==========================================
+ Coverage    94.3%   94.45%   +0.15%     
==========================================
  Files          34       34              
  Lines        6213     6369     +156     
==========================================
+ Hits         5859     6016     +157     
+ Misses        354      353       -1

Impacted Files	Coverage Δ
databricks/koalas/indexing.py	94.4% <100%> (+1.88%)	⬆️
databricks/koalas/series.py	95.46% <0%> (-0.11%)	⬇️
databricks/koalas/missing/groupby.py	100% <0%> (ø)	⬆️
databricks/koalas/missing/frame.py	100% <0%> (ø)	⬆️
databricks/koalas/missing/series.py	100% <0%> (ø)	⬆️
databricks/koalas/frame.py	96.04% <0%> (+0.08%)	⬆️
databricks/koalas/__init__.py	85.36% <0%> (+0.36%)	⬆️
databricks/koalas/testing/utils.py	78.39% <0%> (+0.4%)	⬆️
databricks/koalas/internal.py	96.38% <0%> (+0.5%)	⬆️
databricks/koalas/namespace.py	86.83% <0%> (+0.51%)	⬆️
... and 1 more

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[HyukjinKwon]

Seems okay to me except https://github.com/databricks/koalas/pull/905/files#r333446082

[ueshin]

Otherwise, LGTM.

[softagram-bot]

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