GUI: include and reference `isis_colours.def` and `isis_fonts.def`

As a developer I would like the `isis_colours.def` CS Studio colour definition file to be included with the client so it can be referenced by OPIs. Currently though the OPIs refer to the colour names, they will always use the embedded RGB values as they do not see the file.

The colour file is located in `EPICS\CSS\master\Share` and used by standalone CS-Studio by setting the following preferences
```
org.csstudio.opibuilder/color_file=/CSS/Share/isis_colours.def
org.csstudio.opibuilder/font_file=/CSS/Share/isis_fonts.def
```

It is unclear how to reference them in the GUI - if we could avoid an absolute path that would be good

### Acceptance Criteria
_What is the acceptance criteria?_
- [ ] a
- [ ] b

### Extra Information
_Why it is needed?_

_Where required files/links are_

## How to Test
_verbose instructions for reviewer to test changes
(**Add before making a PR**)_