Script Generator: configurable objects

As a user or script definition maintainer, I would like to be able to define an object for reuse in multiple places in the script generator.

The use case for this was discussed with Max Skoda and others from reflectometry. They currently use MScript to define a number of samples e.g. S1 and S2. Each sample has a set of parameters associated with it to describe how to set slits etc. When creating a script you are then able to select S1 or S2 for an action and the parameters for this sample are used. This avoids constant reinput of the same parameters that can just be associated with the relevant object.

Though we are aiming to fulfil this use case the implementation should remain generalisable for other uses i.e. the object that is defined and actions from those parameters remain defined in the script definition.

Acceptance criteria:

- [ ] I can define an object type outside of a script definition which contains a number of fields that are configurable from the GUI
- [ ] I can configure a number of these objects in the GUI (this should be separate from the script generator action table and hideable from the UI)
- [ ] I can reference these objects from a script generator action
- [ ] The object references are validated (e.g. for our example above only S1 and S2 are valid, this could be implemented as a drop-down if that ticket is done)
- [ ] The script definition run method has access to the fields of the configured object

Notes:

- Please can we not use the word config or configuration when defining terminology for this, it is too overloaded.