Add support for specifying the TransitionCallback and FeedbackCallback outside of initGoal

[finger563]

RIght now the TransitionCallback and FeedbackCallback must be provided every time initGoal is called in order for the callbacks to be called. I'm opening this issue for a PR I will make which will add support for configuring those callbacks outside of the initGoal call.

[finger563]

Would mirror the structure of the SimpleActionSever which allows

void registerGoalCallback (boost::function< void()> cb)
void registerPreemptCallback (boost::function< void()> cb)

so that the SimpleActionClient would have methods

void registerDoneCallback (SimpleDoneCallback cb)
void registerActiveCallback (SimpleActiveCallback cb)
void registerFeedbackCallback (SimpleFeedbackCallback cb)