Store missing keymap for unregistering, and small style cleanup

Hey Pablo, this doesn't fix the 'prints when unregistering' issue, but you were forgetting to append one of the keymap_items.

Also, it's a good practise to unregister things in the reverse order of registering (not sure if Blender does that, but I do it all the time, and I remember correctly you may run into bugs otherwise). 

Finally pep8 suggests 2-white lines between top-level functions/class declarations (class functions have 1 line separation though).