CTF editor cleanup

rename a bunch of stuff
I meant that this could take care of adding `node.center` to `rel_x`, since everyone that uses that has to do
`self.update_node_center(node, node.center + rel_x)`
So, 
```
def update_node_center(self, node, rel_x):
    node.center = clip(node.center + rel_x, self._center_limits)
```