GLMixer Code

Added warning message on invalid file drop in Basket Source.

Compilation fix.

Threaded saving of image (screenshot).

Fixed and improved Camera Shaking FFGL plugin

Change of behavior: do not select all sources when selecting a workspace
in exclusive mode (this was an unexpected and not really useful
feature).

Code cleanup. Using slots for status messages. Improved behavior after
new session (set rendering to match monitor aspect ratio).

Minor GUI improvements in Tooltips and session notes.

Snapshot behavior in views: do not operate on (invisible) sources in
other workspaces when in Exclusive workspace mode.

Behavior improvement on selection of previous and next source.

Implementation of ZOOM gesture on trackpad. BugFix of zoom control in View Render Widget. BugFix in keyboard input of special keys handling (esc and tab).