after refactoring the trk adapter startup, the split was not necessary
any more. in fact, it seemed fairly arbitrary at this point.

each command can have only one of two legitimate responses: "error" or -
depending on the command, and thus declared via a flag - "done" or
"running".
this is way nicer than sprinkling the code with else-ifs (where elses
are sufficient) and asserts all over the place - and silently failing in
release builds.

--tty + outputcollector, working dir and environment setup make sense
only for living local debuggees.

 Fix gdb commands, state changes and signals emissions.
- There were some invalid gdb commands (e.g. "attach").
- There also were a number of unexplected state transitions.

It had unclear semantics and was only used to show a statusmessage.
We do that directly now.

Clean out header.

Intergrate per-engine state tracking with the global running/stopped state.

rename GdbResultRecord into GdbResponse
merge cookie QVariant into GdbResponse
move debugMessage convienience function from individual adapters to base

remove shutdownInferior(), rename shutdownAdapter() into shutdown()