Extension preferences

[gsteinLTU]

Close #1340

This allows extensions to optionally provide a list of toggle-able settings to be added to the menu.

@brollb Should this be called something different from "Options" in the menu, e.g. "Settings", "Preferences"? Where should the structure be documented?

[brollb]

Nice, thanks @gsteinLTU! I have a couple suggestions around naming and the API for extensions:

• So far I have been trying to use classes for the different extension concepts to prevent silent errors due to typos and such (example). This is a bit of a deviation from the style used in other places in Snap (like here). It might be nice to structure this code similarly where there is a class like Option or something which then can configure itself via a builder-esque pattern.
• I would probably name it Settings rather than Preferences but either is really fine.

[brollb]

You may need a pref.toggle.bind(pref) though I imagine it will probably be fine in most cases.

[brollb]

On the topic of documentation, I would add a test here: https://github.com/NetsBlox/Snap--Build-Your-Own-Blocks/blob/master/test/extensions.spec.js

We need to add documentation about extensions. It would probably be nice to add it in the "Development" section of the main docs hosted at https://editor.netsblox.org/docs/. It looks I deleted them during the migration to the new cloud so I will need to add them back...

[gsteinLTU]

@brollb Let me know if the ExtensionSetting class is what you meant. I renamed things to "Settings" in the code, although I think "Options" sounds better in the UI, since they're all boolean (for now?).

[brollb]

LGTM. Thanks, @gsteinLTU!