UI: Allow hiding/unhiding sources in the mixer

Browse Source

Allows the ability to hide/unhide sources in the mixer that the user
doesn't care about or doesn't necessarily want to see (such as video
sources that have audio but don't have any audio playing).  If all
sources are hidden, the user can right-click the mixer's empty area and
choose "unhide all" via a context menu.

Closes jp9000/obs-studio#1002

...

This commit is contained in:

500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f