Fix crash in QObject tree destruction

This issue was discovered while running the QtQuick Controls auto-tests
in valgrind. The issue is that the QObject based property in the VME meta
object is deleted as a child, after its parent (that had the property)
was deleted. At that point it's not safe anymore to emit the notify signal
in the already-deleted object (m_target->object).

Change-Id: I54e81dfedb6e712b8cbf182a72254e33e82910e3
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Initial support for resolving meta-property access for the scope and context objects at QML compile time

This avoids having to do a string lookup for ids and in the import cache at
run-time, before we can do a string hash lookup in the property cache. Instead
we resolve final properties in the context and scope object at compile time and
look them up at run-time using their index instead. The dependencies to these
properties are also tracked separately and recorded in the compiled data.

This is merely the initial patch. There's a lot left to do, such as having
specialized getter and setters for specific property types. Setters are missing
altogether right now and will fall back to name lookup.

Change-Id: If3cb4e7c9454ef4850a615f0935b311c9395b165
Reviewed-by: Lars Knoll <lars.knoll@digia.com>