Fixed symfony:doctrine:schema:drop - added --force

Task symfony:doctrine:schema:drop never actually droped schema because of missing --force parameter.
Added confirmation to doctrine drops tasks

Fixed symfony:doctrine:database:drop (missed --force argument too).
Added confirmation for symfony:doctrine:database:drop and 
symfony:doctrine:schema:drop.
Updated specs for doctrine drop tasks
Merge pull request #319 from solzenic/patch-1

Fixed symfony:doctrine:schema:drop - added --force