GLMixer Code

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).

BugFix: correct color for snapshot rendering.

OSX gui compatibility improvement

Changed terminology for consistency: screenshot is a capture of
rendering, snapshot is a capture of the configuration (snapshot
manager).

Slight improvement of the User Preference dialog for the source
properties: do not show all properties, but a clear (limited) set of
options.

Compatibility of snapshot actions with undo manager.