Motors: show axes are "ready to move"

As a user I would like to know that:

A) Beckhoff: If my relative encoded axis has no errors and has been "homed"
B) Galil: if my power check status is OK
C) all other MCs: if limits are not engaged(?)

I can move a given motor axis.
We could do this by drawing a green border around the motor in the same way we do for whether its in alarm or not.

### acceptance criteria
- [ ] it is made more clear in the above conditions that a motor axis is ready to be moved