Feature: Allow pinning conversations to the top (XEP-0469)

[mercihabam]

This is an implementation of #3509, which allows users to pin bookmarked MUC rooms to the top.

Here is a quick overview of how it looks:

[mercihabam]

Before adding tests for the many changes, I would appreciate a review from the maintainers. Thanks for taking the time to look into this!

[mercihabam]

I went ahead and added tests for the changes. Please review this when you get a chance. Thanks!

[mercihabam]

@jcbrand could you please take a look at this when you get the chance? Thanks.

[jcbrand]

@mercihabam Please rebase your PR onto the latest master branch.

[mercihabam]

@jcbrand that is now done.

[mercihabam]

@jcbrand don't forget this one please. 😊

[jcbrand]

I won't forget, but I'm first finishing off the emoji reactions and popular emojis work. Then I'll make a new release and then I'll get back to all the outstanding PRs.

[jcbrand]

@mercihabam There is a failing test which looks like it might be related to your changes:

Chrome 147.0.0.0 (Linux 0.0.0) A MUC domain group is collapsible FAILED
	Expected true to be falsy.
	    at <Jasmine>
	    at src/plugins/roomslist/tests/grouplists.js:118:52
	    at async UserContext.<anonymous> (src/headless/tests/mock.js:625:13)
Chrome 147.0.0.0 (Linux 0.0.0): Executed 479 of 625 (1 FAILED) (0 secs / 46.029 secs)
Chrome 147.0.0.0 (Linux 0.0.0) A MUC domain group is collapsible FAILED
	Expected true to be falsy.
	    at <Jasmine>
	    at src/plugins/roomslist/tests/grouplists.js:118:52
	    at async UserContext.<anonymous> (src/headless/tests/mock.js:625:13)

Please also squash your commits into one and rebase onto the latest master branch.

[mercihabam]

@mercihabam There is a failing test which looks like it might be related to your changes:

I did not see that one because some tests are skipped on my instance; I'm still figuring out why. But now I have fixed that, rebased onto master, and squashed the commits. Thanks!

[jcbrand]

Thanks @mercihabam, please see my review comments.

[mercihabam]

@jcbrand I have refactored this as discussed. A few tests are now failing, but I will fix them soon. Thanks!

[jcbrand]

Closed in favor of #4088