Rewrote/refactored get_schema to use methods from table classes (GH8232)

Fix creation of database indexes

Tests fix

Fixes

Remove _executefunc

Fixed tests to work with Python3

Schema rewriting

Fixes

Doc update

Fixed postgres schema errors

Fixes

Fixes

Moving if_exists checks to create

Removing executescript

Refactor insert differently

Code review fixes

Removed meta.schema from read_table

Merges

Merged #8208

Replacing izip with zip for Python3
Merge pull request #8232 from artemyk/get_schema_fix

Fix to merge code from `_create_table_statement` and `get_schema`
Eliminating contextmanager based transaction-handling