Pyverdict Support for Postgres, Impala, and Redshift

[jarridrb]

This pull request combines existing pull requests in adding support for postgres, impala, and redshift in pyverdict. All changes allowing for said support are contained herein.

[codecov-io]

Codecov Report

Merging #331 into master will increase coverage by 0.1%. The diff coverage is 63.16%.

@@            Coverage Diff            @@
##           master     #331     +/-   ##
=========================================
+ Coverage      71%   71.09%   +0.1%     
=========================================
  Files         168      168             
  Lines       11485    11504     +19     
  Branches     1873     1874      +1     
=========================================
+ Hits         8154     8178     +24     
+ Misses       2859     2852      -7     
- Partials      472      474      +2

Impacted Files	Coverage Δ
...c/main/java/org/verdictdb/VerdictSingleResult.java	77.78% <ø> (ø)	:arrow_up:
...b/coordinator/VerdictSingleResultFromListData.java	38.03% <0%> (-0.54%)	:arrow_down:
...ctdb/core/aggresult/AggregateFrameQueryResult.java	83.93% <0%> (-1.52%)	:arrow_down:
...inator/VerdictSingleResultFromDbmsQueryResult.java	50% <0%> (-3.33%)	:arrow_down:
...java/org/verdictdb/connection/JdbcQueryResult.java	96.39% <100%> (+0.14%)	:arrow_up:
.../java/org/verdictdb/commons/DataTypeConverter.java	98.89% <100%> (+0.02%)	:arrow_up:
...ava/org/verdictdb/connection/SparkQueryResult.java	55.94% <66.67%> (+0.58%)	:arrow_up:
...a/org/verdictdb/core/aggresult/AggregateFrame.java	85.9% <85.72%> (-0.01%)	:arrow_down:
...verdictdb/core/querying/ola/InMemoryAggregate.java	84.79% <0%> (-2.89%)	:arrow_down:
...or/QueryResultAccuracyEstimatorFromDifference.java	84.16% <0%> (-1.98%)	:arrow_down:
... and 6 more

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[pyongjoo]

Please merge this after updating those port numbers.

I guess two other pull requests will be removed automatically; otherwise, I guess we don't need them since this pull request basically includes them?