Change hotkey to toggle, instead of hold
Change toggle key to Shift+F9 instead of 'F'

This dovetails better with voxel-chunkborder, which now uses unshifted
F9 as of 0.4.1. Requires voxel-keys 0.5.0 since both bindings are
overloading the same virtual key (TODO: shift+, ctrl+ vkeys instead?)
0.5.0