[Shotwell] Improve touchscreen functionality

[Stefan Kuczera <stefan ku gmx de>]

Hi,

I'd like implement a few features to improve touchscreen functionality:

-in fullscreen next photo on left click/single tab; if zoomed go back to
normal view
-in fullscreen previous photo on double tab gesture
-pinch to zoom gesture for touchscreen; centered zoom (zooming around a
center defined by the mouse pointer) seems to exist already

Is there any work out there already that provides these features? I will
probably have some time next week to work on these additions. Also I
would be happy to hear comments on how to implement these features.

/Stefan