Implement Index/MultiIndex.identical

[HyukjinKwon]

This PR implements Index/MultiIndex.identical.

import databricks.koalas as ks
idx = ks.Index(['a', 'b', 'c'])
midx = ks.MultiIndex.from_tuples([('a', 'x'), ('b', 'y'), ('c', 'z')])
idx.identical(idx)
midx.identical(idx)
from databricks.koalas.config import option_context
with option_context('compute.ops_on_diff_frames', True):
    idx.identical(ks.Index(['a', 'b', 'c']))

[HyukjinKwon]

I will add equals after this PR.

[codecov-io]

Codecov Report

Merging #1215 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1215      +/-   ##
==========================================
+ Coverage   95.21%   95.21%   +<.01%     
==========================================
  Files          35       35              
  Lines        7249     7254       +5     
==========================================
+ Hits         6902     6907       +5     
  Misses        347      347

Impacted Files	Coverage Δ
databricks/koalas/missing/indexes.py	100% <ø> (ø)	⬆️
databricks/koalas/indexes.py	96% <100%> (+0.06%)	⬆️

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[HyukjinKwon]

I'm merging for today's release.