Debugger[Trk]: Prepare thread handling.
Store threads and cache registers per thread in Snapshot. As Trk does not generate Thread creation/deletion events. try to add threads on the fly if a stop in a new thread id is reported. Remove them in continue. Continue all threads in classic Trk. Pass on state (crash reason) to ThreadData and model. Factor out common code of both adapters to Snapshot/Symbian classes.