Merge branch 'master' into terencehill/screenshot_viewer

Conflicts:
	qcsrc/menu/xonotic/dialog_multiplayer.c
	qcsrc/menu/xonotic/mainwindow.c
Fix compilation fail
Enhance slide show a bit:
- it continues even if another image is manually selected (with mouse or keyboard)
- seamlessly restarts from the first image after the last image
- can be stopped only by pressing the Slide Show button (or by closing the viewer window)
- Slide Show button stays highlighted while the slide show is active
Add a missing key
Early Lightning Gun, still needs a ton of work. Next step: Remove lightning from electro.
Merge remote branch 'origin/master' into samual/lightning_gun
Lets make the shotorigin work for lightning with everyone involved + some other things.
Merge remote branch 'origin/master' into samual/lightning_gun
Merge remote branch 'origin/master' into samual/lightning_gun
Merge remote branch 'origin/master' into samual/lightning_gun
Cvars for lightning gun
Merge remote branch 'origin/master' into samual/lightning_gun
Merge remote branch 'origin/master' into samual/lightning_gun
Merge branch 'master' into terencehill/screenshot_viewer
Merge remote branch 'origin/master' into terencehill/screenshot_viewer

Conflicts:
	qcsrc/menu/xonotic/mainwindow.c
Disable the preview window as it causes menu to freeze a bit too much when loading high resolution images
Implement zooming
Merge branch 'master' into terencehill/screenshot_viewer
Make possible to move the zoomed-in screenshot on mouse drag
Mouse wheel and -/+ keys to zoom
Also invert the sign of the setZoom input parameter, I think it's cleaner this way