ZOOM PGC: Send encoder settings on Galil power cycle

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.