Added SpaceLogic, to restore the old logic buttons into.
In future it can be used for a more advanced logic editor, with
states, behaviour, whatever. We'll see!
This commit only adds the backend for new space. Committed this
now as reference for when we need another space type. It's still
not well plugin-able (dynamic space types), but my idea is to just
have a new SpacePlugIn for this, with a neat small API to define
all relevant callbacks.
Also note the icon for the spacetype is wrong still.
