Move maintenance banner to top of the screen

[hotzenklotz]

This PR moves the maintenance banner to the very top of the screen as part of the navbar so it does not interfere with other menus / buttons / tabs etc.

The CSS remains mostly untouched. The trick was to use real CSS variables for the navbar height instead of just a LESS variable. These CSS variables can be modified in (JS) code and then the rest of the styles just adapt.
Additionally the current navbar height is also saved in the stored and can be referenced in different downstream methods that used a constant instead.

I also refactored the maintenance banner component a little bit to more clearly separate the data/state from the rendering of the component.

URL of deployed dev instance (used for testing):

• https://___.webknossos.xyz

Steps to test:

• Create new scheduled maintenances
  • e.g. Edit "maintenances" table

INSERT INTO "webknossos"."maintenances"("_id", "_user", "starttime", "endtime", "message", "created", "isdeleted") VALUES('653baadfef0100310a01ec94', '6538f9e0ef0100ef0101ec6d', '2023-11-02 13:03:15.125+01', '2023-11-02 13:50:00.452+01', 'Test Maintenance Banner Foobar Test Maintenance Banner Foobar Test Maintenance Banner Foobar Test Maintenance Banner Foobar Test Maintenance Banner Foobar Test Maintenance Banner Foobar Test Maintenance Banner Foobar ', '2023-10-27 14:19:43.343+02', FALSE) RETURNING "_id", "_user", "starttime", "endtime", "message", "created", "isdeleted";

• Try with a currently active maintenance and a maintenance scheduled in the future

Issues:

• fixes https://scm.slack.com/archives/C5AKLAV0B/p1698066526401089

---

(Please delete unneeded items, merge only when none are left open)

• Updated changelog
• Updated migration guide if applicable
• Updated documentation if applicable
• Adapted wk-libs python client if relevant API parts change
• Removed dev-only changes like prints and application.conf edits
• Considered common edge cases
• Needs datastore update after deployment

[philippotto]

Great stuff 🎉 I like the CSS solution and also the refactoring of the component.
Besides my few comments, I noticed that the ArbitraryView didn't get a listener (like the PlaneView did) even though it uses getGroundTruthLayoutRect. Probably needs to be added?

[hotzenklotz]

I noticed that the ArbitraryView didn't get a listener (like the PlaneView did) even though it uses getGroundTruthLayoutRect. Probably needs to be added?

Good call. Thanks I overlooked this one and will add it.

[philippotto]

Works very well 👍 Thank you for investing time in this 🥇