Fix crash when loading context menu on Windows.

Use QUrl::fromLocalFile to load components from the installation
Qml directory. Using just the absolute file path wasn't a problem
on Linux, but did not work on Windows.

Other Qt modules are also using QUrl::fromLocalFile to do this.

Change-Id: I689c516dc63a6c966435eedb94441d7c9246dd25
Reviewed-by: Andras Becsi <andras.becsi@digia.com>