DBAL second approach

Work in progress.

That's my new approach to making database abstraction layer for Elgg. I'm aiming here to create facade to make core backend-agnostic. For now I'm polishing Elgg_Database_Driver_Default that is equivalent to current version, but aim to support Doctrine DBAL as second backend. Than I want to look at diffrences ti Zend_Db to allow to use it as backend as well. They all should be PDO-similar.

See https://github.com/Elgg/Elgg/issues/4546