Add ability to configure alembic_version table in DialectImpl

Add ability to configure alembic_version table in DialectImpl

Added a new hook to the :class:`.DefaultImpl`
:meth:`.DefaultImpl.version_table_impl`.  This allows third party dialects
to define the exact structure of the alembic_version table, to include use
cases where the table requires special directives and/or additional columns
so that it may function correctly on a particular backend.  This is not
intended as a user-expansion hook, only a dialect implementation hook to
produce a working alembic_version table. Pull request courtesy Maciek
Bryński.

This will be 1.14 so this also version bumps

Fixes: #1560
Closes: #1563
Pull-request: https://github.com/sqlalchemy/alembic/pull/1563
Pull-request-sha: e70fdc8f4e405cabf5099c2100763d7b24da3be8

Change-Id: I5e565dff60a979526608d2a1c0c620fbca269a3f