Make gstreamer-1.0 a required dependency

Testing Done:
Compiled, ran, and sent an IM with a bonjour account with no options, `-Dvv=disabled`, `-Dvv=disabled -Dfarstream=disabled`, and with `-Dvv=disabled -Dfarstream=disabled -Dgstreamer-video=disabled`.

Reviewed at https://reviews.imfreedom.org/r/79/