Replace lib/sql by the cartodb-postgresql submodule

This  commit drops lib/sql contents and replaces it with the cartodb-postgresql repository as a submodule.
No model changes.

The only changes in lib/sql are with making CDB_CheckQuota() function raise a WARNING when _CDB_UserQuotaInBytes() is not found and making the CDB_TableMetadata trigger raise a WARNING when CDB_Invalidate_Varnish() is not found.

\cc @Kartones @javisantana