Add basic plugin metadata for QtQuick2 import plugin.

This indirectly fixes the qdebugmessageservice autotest,
which was getting confused by the "old plugin" warning.
Also updated the extension plugin interface to use
org.qt-project rather than com.trolltech.

Change-Id: I94fc6cf03d23e606c2e2333b013dd2b698f04623
Reviewed-by: Martin Jones <martin.jones@nokia.com>