Android: Added the attribute "extends".

Enables us to detect if a library should be added as a dependency or not.
E.g., libQt5MultimediaQuick_p should only be added as a dependency if an
application is using both QtMultimedia _and_ QtQuick.

Task-number: QTBUG-30861
Change-Id: Id62642c40e2ecca7149d249f65c7b0c950898374
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@digia.com>
Do not call g_type_init() with GLib >= 2.36

g_type_init() is deprecated and the type system is now initialized
automatically.

Change-Id: I5bf5702136cc948dea0a55676dfee2486f12ca00
Reviewed-by: J-P Nurmi <jpnurmi@digia.com>