Port Quick scene preview to QtQuick2.

Also adds zoom using mousewheel and event-forwarding for wheel events,
which wasn't possible with QtQuick1 due to missing wheelevent-support.
Fix crash when an QuickItem's parent is set to 0.

The itemreparented-slot now checks if the parent was set to 0
(=> removed from the scene, without deleting) and in this case removes
the item from the model.
QuickItemModel: Remove children of removed items.

This commit fixes a crash when accessing the children of an item whose
parent has been removed from the model. Until now the children
remained in the model's internal data set, now they're removed
correctly, when the parent is removed.
Add class to represent a probe ABI, and to find a matching one.
Empty stub of the probe ABI detector.

Apart from the dummy implementation (which is functionally equivalent to
the current behavior), we can't actually detect anything yet though, on
any platform.
Add convenience API to check if the Qt version is set.
Add caching of probe ABIs for QtCore DLLs.
Implement QtCore version detection for ELF, and detecting QtCore for a PID.

We currently have two ways of detecting the version:
- the file name
- the version printed when executing QtCore.so

For detecting QtCore for a given PID we only support /proc lookup at the
moment, a non-/proc fallback as we have it in the process list still needs
to be added.
Add architecture detection for ELF.
Add ldd-based detection of QtCore DLL used by a executable.
Start to use GammaRay::ProbeABI in the ProbeFinder API.
Add a method to get the absolute executable path, for ABI detection.
Run the probe ABI detection, if no ABI is specified explicitly.
Pick the best available probe.
Add operator== for GammaRay::ProbeABI.
Auto-detect the ABI when picking an executable on the launcher page.

Also use the nicer display names for the probe ABIs in the UI.
Find QtCore on Mac, using otool and lsof.
Add architecture detection for Mach-O files.
Refactor Mach-O parsing to prepare for reading load commands.
Read Mach-O load commands to obtain the QtCore version number.