Change motor internals to better match ophyd

[DominicOram]

To ease in migration it would be good if the underlying signals in Motor had the same name as EpicsMotor. For example, user_readback in EpicsMotor is readback in Motor. We should go through and try and keep consistency unless there is a good reason to change the name.

Additionally, there are a number of parameters that are not exposed:

• Limits (see Helper to check against motor limits #41)
• Acceleration

[DominicOram]

I think I might have changed my mind that we need to keep internal signal names the same. It's only a minor change from ophyd

[DominicOram]

Discussed offline, attribute names should match as much as possible

[DominicOram]

It would also be good to add the fields we're missing in DiamondLightSource/hyperion#1235