Removal of automatic exception catching.

This is an issue to track removal of automatic exception catching. Currently BFTask continue* methods automatically catch exceptions, unless you disable them via BFTaskSetCatchesExceptions().

This functionality leads to inconsistent behavior and big memory leaks, because ARC by default is not going to cleanup the memory that was not released at the time the exception was thrown. As an improvement to the API and consistency with Bolts-Swift - we are removing automatic exception catching from Bolts-ObjC.

Currently planned version that this will be removed in is 1.9.0.