Add diagonal gesture support
Add option to enable/disable diagonal gestures (default: disabled)
Fix cases where too-precise (varying less than 10px) LRUD movement not registered
Add pseudo-"antialiasing" to reduce unintentional gesture recognition
Add usediagonals string to all locales

At the moment only en-US, de and fr have proper localisation. All other
locales use the English string and need translation. This is working
under the assumption that correct non-localised text is better than
poorly translated localised text (e.g. from Google Translate).