More device debugging at startup

* List all axes found
* Be explicit about devices which get skipped
* Log a warning if there are no devices with >1 axes
  - Gdk reports all non-"fancy" devices' axes as Gdk.AxisUse.IGNORE now :(
  - Mice and touchpads aren't fancy enough, seemingly
  - Don't know yet if tablets that have problems do this (see #29)
  - Let's find out!