Fix a few initialization order warnings.
Properly support Qt5 in the message handler.

This avoids losing the message context, and avoids triggering the recursion
detection fallback when daisy-chaining message handlers. This also fixes
the missing newlines in the console output as that's a missing in the
recursion fallback code in Qt.
Silence Clang warning about missing parenthesis around logical operations.
Fix QGV scene selection in in-process mode.
Cleanup parentObject(), QQ2 specific handling is now in its own tool.
Unify the implementation of the object list and tree models.

Just like the tree model, we now use the infrastructure for multi-thread
support from Probe, rather than rolling our own. This also means we are
now back to a recursive mutex, which fixes a deadlock when requesting
the decoration role on the list model (due to an internal temporary QFile
during icon loading).
Document objectCreated/objectDestroyed.

There's a few non-obvious implications in multi-threaded applications to
consider here.
Remove obsolete workaround that causes unnecessary warnings nowadays.
Ensure all ancestors are known, not just the immediate parent.

This fixes a crash when showing tooltips in Qt5 applications.
Merge remote-tracking branch 'origin/2.1'
Introduce signal monitor tool

This tool provides an interactive of QObject signals. It's still work in
progress, some major features still need to be implemented:

  - display of time marks in the event view
  - print signal names as tooltips and in the graph if sufficient space
    is available
  - interactive range selection
  - timestamp rubberband
  - ...

SignalHistoryModel::Item also might need cleanup.
Improve colors in the signal monitor and restore selection
Remove debugging left-overs
Show tooltips for signal history
Don't show horizontal scrollbar for event view

Let's not show it by accident. We have our own, custom one.
Optimize layout compution for the event history
Use better formula to find event tooltips
Simplify time management in signal history

Introduce RelativeClock class to manage application start offset.
Add label for the signal monitor's zoom widget
Extract SignalHistoryView from SignalMonitorWidget

I need to capture more widget events and doing all this redirections
in SignalMonitorWidget would become ugly.