Implement edge long swipe gesture [1/3]

The gesture will activate if user executes edge swipe for a long
horizontal motion. The triggered action is configurable in Button
Settings.

Reference:
https://gerrit.dirtyunicorns.com/q/topic:%22back-longswipe-actions%22

Change-Id: Ie1bbe6645b6a00d346af60d6bb5e4d584997d6e9