GitLab

These only work with gitlab.com and not other instances.

The latter only contains some plugins now, all bindings for writing
applications and plugins is included in gstreamer-rs now.

gstreamer-rtsp-server and gstreamer-editing-services are disabled for
now until there's a new release of them, or once we start building
against git master of them.

Fixes #16

Solves two issues from #16

This is also getting us rid of bitflags.

The ABI tests are not all succeeding yet.

By default, pkg-config-rs sets the PKG_CONFIG_ALLOW_SYSTEM_LIBS
environment variable
(https://github.com/alexcrichton/pkg-config-rs/pull/35), which leads
to eg /usr/lib being present in the middle of the final command,
in turn leading to issues when working in an uninstalled environment,
where libraries that are also present system-wide do not get linked
against.