Make use of $$MODULE_PLUGIN_TYPES

This fix build after 48b107ecfe216b93361ee162999e0cd0ee1cee41

Change-Id: I9baacd384e280736c8cb05150bb14ac5549be62f
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>
Minor clean-up for plugin .pro files

Change-Id: Ie17a754db273154f8579a508a244272fb4c0a73f
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>