Add validator for TenantMixin.schema_name, check for 'pg_' prefix
Make schema_exists case insensitive
Merge pull request #181 from rev112/fix_case_insensitive_schema_name

schema_exists now case insensitive
Merge pull request #175 from rev112/schema_name_validation

Added validator for TenantMixin.schema_name, check for 'pg_' prefix