Minor: Improve error reporting
Free SHM as soon as we dont need it anymore

If gammaray-client hangs (for whatever reason), it's parent process, the
launcher is still alive and doesn't release the SHM segment it owns. The
same happens when the launcher application crashes -- the SHM segment is
not released.

Each QSHM holds a QSystemSemaphore, and number of accessible semaphores
on a Unix system is very limited (128 is the upper limit).

If you've finally reached this limit, you can't create more SHM segments
and hence cannot start a GammaRay instance anymore.
You end up with this message:

void GammaRay::Launcher::sendProbeSettings() Failed to obtain shared
memory for probe settings: "QSharedMemoryPrivate::initKey: unable to set
key on lock" - error code (QSharedMemory::SharedMemoryError): 7