Merge pull request #18059 from davidflanagan/camera-preview

Bug 989361: better swipe handling for switching items in preview r=justindarc(cherry picked from commit fb29a8ea2d79c56cf2dda54ce2056e7e53644243)

Conflicts:

	apps/camera/test/unit/controllers/preview-gallery_test.js
Merge pull request #18245 from davidflanagan/camera-preview-v1.4

Merge pull request #18059 from davidflanagan/camera-preview