package/wpewebkit: add option to enable media-stream

This has a compile time dependency on gst1-plugins-bad due to
the codecparsers dependency.

We need to prevent the wpe plugin from being selected when wpewebkit
media-stream support is enabled as the wpe plugin requires wpewebkit
which would create a circular dependency with gst1-plugins-bad.

Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>