Make StatusWidget tools dropdown extensible

[rafaucau]

Changes proposed in this pull request:

This PR allows you to more easily modify the tools dropdown in the StatusWidget component using ItemList.

Until now, if you wanted to add something to this dropdown, you had to push a child:

 extend(StatusWidget.prototype, 'items', (items) => {
    const tools = items.get('tools');
    tools.children.push(<Button>Test</Button>);
  });

If you want to remove / replace a given item it gets harder.
Now such code is enough:

 extend(StatusWidget.prototype, 'toolsItems', (items) => {
    items.add('test', <Button>Test</Button>);
  });

Reviewers should focus on:

Confirm that everything works.

Screenshot

Necessity

• Has the problem that is being solved here been clearly explained?
• If applicable, have various options for solving this problem been considered?
• For core PRs, does this need to be in core, or could it be in an extension?
• Are we willing to maintain this for years / potentially forever?

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Core developer confirmed locally this works as intended.
• Tests have been added, or are not appropriate here.

[davwheat]

Thank you for the PR! Just some minor comments from me.

I know @askvortsov1 doesn't want many changes to the Admin dashboard at the moment, since it'll be getting a rewrite in the near future, so I'd appreciate his input.

Personally, I think we can make changes up until v1.2. That way, when rewriting, we can use the existing dashboard as a benchmark to ensure features or extensibility aren't accidentally dropped between the two, and to make the overall migration easier.

[davwheat]

Also it looks like you've rebased this incorrectly, as there are some changes to the file versioner since I began writing my review. Could you make sure those are fixed, too?

[rafaucau]

Also it looks like you've rebased this incorrectly, as there are some changes to the file versioner since I began writing my review. Could you make sure those are fixed, too?

@davwheat Uhhh, managed to fix my commits. Sorry for that 🤦‍♂️

[askvortsov1]

We might change things eventually, but for now I'm glad for this to be more extensible.