Don't require applications to declare metatypes.

These metatypes need to be declared for common usage of the positioning
API. Declare them in the library header files so that applications are
not forced to do so.

[ChangeLog][QtPositioning][General] Applications no longer need to
register common Qt Positioning data types with the metatype system.

Change-Id: I1d28ec8e33d20efc748cb6a0a2ad302e2061853f
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>