libglom: Add escape_sql_id() and use it for table add/drop/rename.

* glom/libglom/db_utils.[h|cc]: Add escape_sql_id(), using
gda_connection_quote_sql_identifier().
create_table(), rename_table(), drop_table(): Use it instead of
manually adding quotes with no escaping.
* tests/test_selfhosting_new_then_alter_table.cc: Mention that
the commented-out test still fails because of libgda bug #663608 .