[sql lab] quote schema and table name

[mistercrunch]

fixes #4595, basically handling table names with spaces or special characters in them

[codecov-io]

Codecov Report

Merging #5195 into master will increase coverage by <.01%.
The diff coverage is 80%.

@@            Coverage Diff             @@
##           master    #5195      +/-   ##
==========================================
+ Coverage   63.45%   63.46%   +<.01%     
==========================================
  Files         261      261              
  Lines       19822    19825       +3     
  Branches     1989     1989              
==========================================
+ Hits        12579    12582       +3     
  Misses       7234     7234              
  Partials        9        9

Impacted Files	Coverage Δ
superset/models/core.py	86.56% <100%> (+0.02%)	⬆️
superset/db_engine_specs.py	53.87% <75%> (+0.15%)	⬆️

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[gbates101]

Nice. Better solution than what I proposed.

[mistercrunch]

Ended spending time trying to use sqlalchemy.table (not schema aware) and sqlalchemy.Table which requires Metadata context, which didn't work at well. Finally figured out how to get the quoting function of the dialect.

[mistercrunch]

@betodealmeida @john-bodley