OFFSPEC: add front bench

[rerpha]

As a scientist I would like my front bench to track the beam, currently without a supermirror but in the future using one.

This is currently already in their config as a component, but no parameters or drivers have been set up:
https://control-svcs.isis.cclrc.ac.uk/git/?p=instconfigs/inst.git;a=blob;f=configurations/refl/config.py;h=7755591719e46bc6e8b715334f5ec1d92fa20c51;hb=refs/heads/NDXOFFSPEC#l134

Basic motion commissioning and testing is essential before this work starts as it's the front bench has not moved for a long time.

There will likely be a slot for doing this at the end of the March 27 cycle.

acceptance criteria

• offspec front bench motion (two jacks and horizontal slide) are recommissioned
• reflectometry configuration is updated to add the parameters for angle,offset and seesaw
• reflectometry configuration is updated to add drivers for the two jack axes and the horizontal slide. Unlike the rear bench this does not have a Chi axis as it doesn't rotate.

Notes:

• future work will involve adding a liquid mode and also recommissioning the supermirror and adding it to the reflectometry configuration. time estimates on this are unclear.
• especially without a supermirror, the bench should follow the same max/min angles as the rear one, but it's pivot point is the supermirror Z position rather than the sample point.