EventKernel, etc: Making setSignalState non-const.
Change the ISignalState::setSignalState and resetSignalState methods to be (properly!) non-const. SignalStateHelper now takes a non-const pointer to the object. (Temporarily?) introduce SignalStateConstHelper that takes a const pointer and does a const_cast on it; this is marked as not thread-safe.
Remove now-unused SignalStateCollHelper.
Corresponding changes downstream.