Session contains a set of 'Batch' that are created in the Player (renamed from PlayGroups). Session InputCallback can now target either a Source or a Batch, using std::variant (new type Target). Input Mapping reacts to input to create callbacks to a target, either a single source (as before) or to a Batch (multiple sources).
When a source in a session fails, it is not anymore deleted after update; the Mixer keeps it in the session but detaches it from the scene. This way the user can access the failed source in the navigator (listed in RED), and Replace the source. The Replacement of source is available for any source. The source visitor does not skip a visit if the source failed.
Add play/pause button on source icon in selection (dynamic or stored selection). Display source icon in lower left corner, instead of play status. Fix alignment disabled timeline. Minor bugfix.
Replace the 'inspector' menu in favor of a magnifying glass button at top right corner of imgui window for Player and Output preview. Disable the magnifying glass upon window unfocus.
Unified menu in output window for streaming (for SRT, Shmdata and peer to peer). Cleanup SRT broadcaster and bugfix on FrameGrabber default frame timing.
