SXD: OPI for Foil Changer

As a SXD scientist I want to be able to control the foil changer, so that I can control the foils used in my experiments.

**Note:** it is likely that this ticket will not be needed - see notes below.

#### Acceptance Criteria
1. Using the IBEX client, I can control the foil changer.
1. Using the genie_python, I can control the foil changer.

#### Notes
1. Check the [SXD Instrument wiki](https://github.com/ISISComputingGroup/IBEX/wiki/SXD-Instrument-Details).
1. The OPI must offer functionality equivalent to the existing VI (located here: `C:\LabVIEW Modules\Instruments\SXD\SXD Foil Changer`).
* The Foil Changer is controlled by LinMot drives.
* This is a very odd VI. It appears to do no more than control comms settings.
1. **Note from Instrument Scientist:**
* SXD foil changer: I don’t know what this is supposed to be. It sounds like something that is used on VESUVIO.