frontend: Improvements on MiniVideoRecorder

[ArturoManzoli]

Current behaviour

1. When one Mini VIdeo Recorder starts processing its own video, the other instances get the 'processing state' animation as well.
2. Each Mini Video Recorder can only control one stream.

Expected or desired behaviour

1. The processing visual feedback should be independent for each stream or at least, the animation should not cover the video recording duration on the widgets that are currently not processing any video.
2. One single Mini Video Recorder should be capable of controlling more than one stream. On the stream selection dialog, user could have checkboxes to choose more than one stream to be recorder at the same time.

Prerequisites

• I have checked to make sure that a similar request has not already been filed or fixed.