Blender Git Loki

Keymap: cycle space-subtypes on successive presses

Some space types are exposed as multiple space types,
previously the key binding to set the space type would use the last
used space-type.

Now pressing the key again cycles to the next space sub-type.

Without this, shortcut display is confusing since some space types share
a key. Keymap display will need to be updated to support this.