Refactor according to last DBAL changes

Recently, we have move all adapters classes to the driver namespace & refactored the query debugging in the DBAL. Instead of using Monolog, we now use the Symfony2 event dispatcher. As the bundle still rely on the Monolog implementation, It needs to be refactored too.

To resume, this PR does the following things:

 * Remove Monolog & rely on the Symfony2 Event Dispatcher
 * Fix travis config
 * Add PHPUnit as require-dev
 * Fix the command tests according to the last change in Symfony