pipeline: stop setting the track caps
requested to merge hwilkes/gst-editing-services:stop_setting_track_caps_after_construction into master
Stop setting the track 'caps' property. The previous code could overwrite a users own setting of the caps for video and audio caps. Moreover, the 'caps' property is listed as construct only, and users will likely expect it to stay the same after a track has been added to a timeline.