Replaced the collision states defines

ACTIVE_TAG = 1,
ISLAND_SLEEPING = 2,
WANTS_DEACTIVATION = 3,
DISABLE_DEACTIVATION = 4,
DISABLE_SIMULATION = 5

With an enum, thus validating at compile time that

setActivationState(), forceActivationState() calls always receive valid arguments.
Also, changed the demo application and btRigidBody to reflect the change.