Adding Coverflow and Timeline Application Switchers

Controls are currently the same for all switcher styles:
- Bind 'switch-panels' switches between all windows
 - For example Ctrl + Alt + Tab
- Bind 'switch-group' switches between all windows of the same app
 - For example Super + Tab
- All other binds default to all windows of the same workspace
 - For example Alt + Tab
- Pressing Ctrl +left or right during selection switches workspace.
- Clicking on an icon or preview activates it
- Clicking somewhere else aborts the switcher
- Escape aborts the switcher
- Enter activates the current selection
- Pressing D during selection shows the Desktop.
- Pressing Q during selection closes the current window (switcher stays active)
- Pressing Arrow keys navigates through the list
 - Holding Shift while using arrow keys navigates the list in reverse order.
- Scrolling the mouse wheel navigates through the list

Additional Credits go to p91paul and dmo60 for the original coverflow code.