Add a 'display.max_rows' configuration with typed configuration support

[HyukjinKwon]

This PR:

1. Expose get_option, set_option, reset_option to koalas namespace
2. Add typed values supported by JSON ser/de
3. Convert max_display_count variable to display.max_rows option.

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Softagram Impact Report for pull/714 (head commit: a998b12)

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[codecov-io]

Codecov Report

Merging #714 into master will increase coverage by 1.77%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #714      +/-   ##
==========================================
+ Coverage   92.41%   94.18%   +1.77%     
==========================================
  Files          32       32              
  Lines        5548     5559      +11     
==========================================
+ Hits         5127     5236     +109     
+ Misses        421      323      -98

Impacted Files	Coverage Δ
databricks/koalas/generic.py	93.71% <ø> (-0.04%)	⬇️
databricks/koalas/series.py	95% <100%> (+0.01%)	⬆️
databricks/koalas/__init__.py	85% <100%> (+8.07%)	⬆️
databricks/koalas/config.py	100% <100%> (ø)	⬆️
databricks/koalas/indexes.py	97.22% <100%> (+0.02%)	⬆️
databricks/koalas/frame.py	94.84% <100%> (+0.01%)	⬆️
databricks/koalas/internal.py	96.29% <0%> (+0.46%)	⬆️
databricks/conftest.py	97.67% <0%> (+4.65%)	⬆️
databricks/koalas/usage_logging/usage_logger.py	100% <0%> (+50%)	⬆️
... and 1 more

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[HyukjinKwon]

@ueshin, let me merge this one to unblock #715