Disable probe widgets under QNX

It is assumed that GammaRay for QNX is always cross-compiled. Exibting the
GammaRay UI on the target does not make sense, and prevents the actual target
application UI from appearing.
Style nitpick: const& instead of just &
Synchronize KLinkItemSelectionModel with upstream.

This includes the fix commited in Review 111953 which adds proper
support for synchronizing the currentIndex. Potentially this fixes
bugs in Gammaray, like the oscillation of the remote selection model.
Merge branch 'master' into remote-fontbrowser