effects/desktopgrid,overivew: set touchpad gestures to match 5.24

As we don't provide any ability for the user to configure the gestures yet, the gesture for the desktop grid should stay as it was in the last release. This commit swaps the gestures for desktopgrid and overview to achieve that.

I don't know how to best add the ability for scripted effects to register touchpad gestures, so I left the show desktop gesture out for now.

cc #93 (closed)