ZOOM PGC: Send encoder settings on Galil power cycle

[DominicOram]

As a scientist on ZOOM I would like to be able to reliably move the PGC. The PGC uses absolute encoders and to set them up after a power cycle the following code has to be sent:

SYA=0
SSA=1,26,27,0<15
SYB=0
SSB=1,26,27,0<6

This was previously done using premove commands but the commands are too long to be put in the premove string.

Acceptance Criteria

• The above is sent on every Galil restart (or more often if easier)
• https://github.com/ISISComputingGroup/ibex_developers_manual/wiki/Motors-Trouble-Shooting#zoom-pgc is moved out of troubleshooting into somewhere more sensible.

[FreddieAkeroyd]

SYA=0;SSA=1,26,27,0<15 doesn't look too long for MTR0101.PREM - or do A and B not refer to axes and both parts need to be sent to the axis?

[FreddieAkeroyd]

Though I have a feeling that sending them every move on IMAT might have caused issues. MTR0101.INIT might be a good place, but i can't remember if that field is used by the Galil driver.

[DominicOram]

Only one of the axes moves so both parts were being sent in the same string

[DominicOram]

What I have done for now is set the PREMOVE string to just be SYA=0;SSA=1,26,27,0<15; this will ensure that the first encoder always works. The second one is just a backup anyway so whilst it would be good to get it sorted it's not required for running the instrument.