Database: PgSqlDriver reflection search in all current schemas

Partially solves #1101.

This is without BC break. Limitations of multiple schemas using overview:
- must call `SET search_path TO schema1, schema2, schema3`
- table must be named uniquely across all schemas

Related problem (http://forum.nette.org/cs/14487-postgresql-automaticke-cmuchani-cizich-klicu)