Implement Series.plot.box with plotly

[HyukjinKwon]

This PR implements Series.plot.box with plotly. Note that DataFrame.plot.box is not already supported in Koalas yet.
This can be tested via the link: https://mybinder.org/v2/gh/HyukjinKwon/koalas/plot-box-ser?filepath=docs%2Fsource%2Fgetting_started%2F10min.ipynb

Note that you should manually install plotly to test with mybinder above:

%%bash
pip install plotly

Example:

# Koalas
from databricks import koalas as ks
ks.options.plotting.backend = "plotly"
kdf = ks.DataFrame({"a": [1, 2, 3, 4, 5, 6, 7, 8, 9, 15, 50],}, index=[0, 1, 3, 5, 6, 8, 9, 9, 9, 10, 10])
kdf.a.plot.box()

# pandas
import pandas as pd
pd.options.plotting.backend = "plotly"
pdf = pd.DataFrame({"a": [1, 2, 3, 4, 5, 6, 7, 8, 9, 15, 50],}, index=[0, 1, 3, 5, 6, 8, 9, 9, 9, 10, 10])
pdf.a.plot.box()

For the same reason as #1999, the output is slightly different from pandas'.
I referred to "Box Plot With Precomputed Quartiles" in https://plotly.com/python/box-plots/

[HyukjinKwon]

This PR is dependent on #2006

[codecov-io]

Codecov Report

Merging #2007 (4d82385) into master (d0f4ad2) will increase coverage by 0.00%.
The diff coverage is 96.29%.

@@           Coverage Diff           @@
##           master    #2007   +/-   ##
=======================================
  Coverage   94.57%   94.58%           
=======================================
  Files          50       50           
  Lines       11142    11192   +50     
=======================================
+ Hits        10538    10586   +48     
- Misses        604      606    +2     

Impacted Files	Coverage Δ
databricks/koalas/plot/plotly.py	96.05% <94.44%> (-1.68%)	⬇️
...ricks/koalas/tests/plot/test_series_plot_plotly.py	98.05% <100.00%> (+0.41%)	⬆️

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[HyukjinKwon]

I tired hard but couldn't figure out how to remove this 0 .. 😢
(in the PR description)

[HyukjinKwon]

this is ready for a review.

[HyukjinKwon]

BTW, Koalas boxplot will additionally also show the mean value (dot dash line) unlike pandas':

[ueshin]

LGTM.

[ueshin]

Thanks! merging.