Support custom Control Options

[tom-writes-code]

Allow users to edit the control options they see on screen

Work in progress:

I think I'd like a new table to go with this to set:

• A firmwide default set of control options
• An individual user default set of control options
• Specific control options for a single snippet

[tom-writes-code]

This needs documenting and properly testing in anger before I merge it.

A fallback control statement of ctl-opt; is provided

Users can override this system default for a single snippet

Users can also override this system default and save that as their personal default

Whenever a repl session is loaded, then a control statement is found by checking in the following order:

1. Is there already a control statement linked to this session?
2. Is there a user default control statement?
3. Is there a system default control statement?
4. Return ctl-opt;

• I intentionally haven't provided a way of setting the system/organisational default, but I will provide documentation instructions.
• I need to test how this works with saving and loading snippets

There is also no method of removing your user default for good. This feels like a niche requirement at the moment.

[tom-writes-code]

The generated source puts the ctl-opt statements in a predictable location