Support None to unlimit 'display.max_rows'

[HyukjinKwon]

This PR adds the support to unlimit the number of rows at 'display.max_rows'.

>>> import databricks.koalas as ks
>>> ks.set_option("display.max_rows", None)
>>> ks.range(1001)
        id
0        0
1        1
...
1018  1018
1019  1019

[1020 rows x 1 columns]

[HyukjinKwon]

shortcut_limit cannot support None as at least it needs empty dataframe to infer its type when its needed.

[softagram-bot]

Softagram Impact Report for pull/742 (head commit: f7d979c)

⭐ Change Overview

(Open in Softagram Desktop for full details)

📄 Full report

• Permalink: Full report for pull/742

Impact Report explained. Give feedback on this report to [email protected]

[codecov-io]

Codecov Report

Merging #742 into master will decrease coverage by 2.35%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #742      +/-   ##
==========================================
- Coverage   94.03%   91.67%   -2.36%     
==========================================
  Files          32       32              
  Lines        5650     5659       +9     
==========================================
- Hits         5313     5188     -125     
- Misses        337      471     +134

Impacted Files	Coverage Δ
databricks/koalas/config.py	100% <ø> (ø)	⬆️
databricks/koalas/series.py	95.02% <100%> (-0.17%)	⬇️
databricks/koalas/indexes.py	97.29% <100%> (+0.07%)	⬆️
databricks/koalas/frame.py	94.53% <100%> (-1.7%)	⬇️
databricks/koalas/usage_logging/__init__.py	23.14% <0%> (-74.08%)	⬇️
databricks/koalas/usage_logging/usage_logger.py	50% <0%> (-50%)	⬇️
databricks/koalas/__init__.py	77.5% <0%> (-7.5%)	⬇️
databricks/conftest.py	90.69% <0%> (-6.98%)	⬇️
databricks/koalas/namespace.py	79.66% <0%> (-1.34%)	⬇️
... and 5 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 625cea6...f7d979c. Read the comment docs.