Use Postgres function to_regclass to check for existence of table

[aashikgowda]

Checklist

• I have read the Contributing Guide
• I have checked to ensure this does not introduce an unintended breaking changes
• I have considered appropriate testing for my change

Description

• Addresses Check for journal table existence slow on large PostgreSQL instance. #2.
• Uses Postgres function pg_catalog.to_regclass to check for a table's existence. The performance is not dependent on the size of the user data tables in the database.
• Versions prior to Postgres 9.4 will not be able to support this functionality and 9.3 reached end of life in 2018.
• Fixed another issue where single quotes were not allowed in schema and table names.