Created a new battlecry system.

Battlecries now work with the tag system, like deathrattles and effects.

The old system is still supported while in transition, but all new cards
will be created using the new battlecry system.

Also implemented a choose mechanic and switched all Druid minions

Implemented Antique Healbot and Anodized Robo Cub as test cases for
the new system.