Visualization Unicode bug fix

[JamshedRahman]

This change fixes unicode data errors in Python 2. Replacing str() with six.text_type(), which is unicode() in Python 2 and str() in Python 3.
This change is an extension of #5093 for all viz types.
Also includes an unit test for time series viz types.

[JamshedRahman]

This build is failing due to an unrelated issue. Looks like #5236 and #5357 are creating a conflict due to duplicate keys in controls.jsx line 211. Please fix controls.jsx...

[mistercrunch]

LGTM, can you rebase please. I think master may have been broken at the time you created your branch.

[codecov-io]

Codecov Report

Merging #5387 into master will not change coverage.
The diff coverage is 0%.

@@          Coverage Diff           @@
##           master   #5387   +/-   ##
======================================
  Coverage    59.1%   59.1%           
======================================
  Files         372     372           
  Lines       23747   23747           
  Branches     2758    2758           
======================================
  Hits        14036   14036           
  Misses       9696    9696           
  Partials       15      15

Impacted Files	Coverage Δ
superset/viz.py	77.34% <0%> (ø)	⬆️

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[JamshedRahman]

Updated and resubmitted. @mistercrunch please merge to master when you get chance :-)

[mmuru]

@JamshedRahman: Please, can you add the following change into your PR. The issue #5479 has more details
Line 753 in superset/models/core.py sqls = [str(s).strip().strip(';') for s in sqlparse.parse(sql)] should change to sqls = [six.text_type(s).strip().strip(';') for s in sqlparse.parse(sql)]
I tested this change and worked.

[mistercrunch]

Ooops, noticed the new comment after merging. It should be able to create a new PR with that change.