Network preference for the order of communities in the dashboard and dropdown

[MoshiKoi]

First take at #1323, testing and feedback welcome

This PR adds a new preference type for the community preference, as well as a separate "block preference" for styling purposes since it didn't make much sense trying to cram it into the horizontal layout the other preferences use. The styling is very much a work in progress, but it is functional right now.

You can reorder the communities by dragging. I pulled in JQuery-UI for this - not entirely sure if it's worth bringing it in as a dependency, but it can be replaced if needed. I have switch to SortableJS to avoid depending on jQuery.

Might try to also implement "collapsed" communities (#1993). Not sure if that has any real added value if it just sends communities to the bottom since users can do that anyway, but it might be useful as a foundation for later work if we want users to, for instance, be able to set up an email subscription of "posts from focused communities" or similar mechanism.

[codecov]

Codecov Report

❌ Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.11%. Comparing base (1ab1ddf) to head (60c9c99).

Files with missing lines	Patch %	Lines
app/controllers/application_controller.rb	0.00%	1 Missing ⚠️
app/models/community.rb	85.71%	1 Missing ⚠️

Additional details and impacted files

Components	Coverage Δ
controllers	76.98% <0.00%> (ø)
helpers	85.47% <ø> (ø)
jobs	77.43% <ø> (ø)
models	93.22% <85.71%> (-0.03%)	⬇️
tasks	61.11% <ø> (ø)
scripts	∅ <ø> (∅)

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[trichoplax]

I like the draggable handles. I think for many people that will be the easiest way to rearrange the communities. Could we keep the handles and also add up and down buttons (that shift that community one place in that direction)?

Some people may find up and down buttons more convenient, but also some people cannot drag (for various reasons).

See Dragging Movements accessibility guidance.

If both draggable handles and up and down buttons take up too much space, there's also the possibility of having up and down buttons only appear when a draggable handle is clicked/tapped rather than dragged. Personally I'd prefer up and down buttons that are always visible to aid discoverability.