Database introspection: fdb schema api

[maxirobaina]

Evaluante replace plain sql schema introspection by fdb schema api.

http://pythonhosted.org//fdb/usage-guide.html#working-with-database-schema

Working with database schema
Description of database objects like tables, views, stored procedures, triggers or UDF functions that represent database schema is stored in set of system tables present in every database. Firebird users can query these tables to get information about these objects and their relations. But querying system tables is inconvenient, as it requires good knowledge how this information is structured and requires significant amount of Python code. Changes in system tables between Firebird versions further add to this complexity. Hence FDB provides set of classes (isolated in separate module fdb.schema) that transform information stored in system tables into set of Python objects that surface the vital information in meaningful way, and additionaly provide set of methods for most commonly used operations or checks.