ui: Dependency Upgrade

[johncowen]

This PR is ontop of our ember update to 3.8 and upgrades everything else (apart from ember-exam)

Interesting things of note:

1. We switched all the new lint errors to warnings, we basically put off fixing these until a later date. Running the app now gives you lots of yellow warning messages to annoy, so they will be looked at fairly soon.
2. We removed dart-sass which we weren't using but was left in there from an experiment from many moons ago 😮 !
3. We removed a few other things which we don't use but are probably there from when we originally copied our starting skeleton from elsewhere.
4. The jquery resolution is no longer needed, the upgrade pushes us into 3.4 (plus we hope to remove jquery entirely soon)
5. We use a slightly custom href-to helper to globally fix wildcard URL encoding for ember wildcard routes (see UI: [BUGFIX] Decode/encode urls #5206). This needed altering slightly as a result of the upgrade, as a bonus we're aware that ember-href-to now supports sticky query params 🎉

We've left ember-exam without upgrading here potentially @alvin-huang might want to do that, or at least I need to check with him that the upgrade will be good for CI - probably to be done in a later PR.

[backspace]

I see that you want to address these later but I think this one would be as simple as an else { return undefined; }

[alvin-huang]

I can follow up with you on the ember-exam upgrade, without testing the command myself and just looking at the latest releases, it looks like the current command in CircleCI should just work still.

[johncowen]

@alvin-huang ah thanks for looking, thats cool then if it all looks good to you, I added a commit on the end here, everything continues to pass 🎉 , thankyou!

[johncowen]

Closing in favour of #6452