Add ability to manually remove or exclude a source

[sayhiben]

Overview Sometimes, the livesheet or custom source list contains sources that the streamwall user is not interested in using, and they become noise to filter through when running streamwall. We should add the ability to remove or exclude sources.

Acceptance Criteria

• Sources from the livesheet can be hidden
• Hidden livesheet sources can be unhidden (perhaps there's a second "tab" or out-of-sight area that lists hidden sources)
• Custom sources can be removed entirely
• Removing or hiding a source also removes instances of that source from the streamwall grid