Ranking/Leaderboard ViewModel

[gruvw]

Fixes #299

Ranking/Leaderboard ViewModel

This PR aims to bring real user data from the database into the view of the leaderboard/ranking page.

Waiting on #319 and #322 to be merged before integration of viewmodel inside view.

Acceptance criteria

• [x] Retrieve users that have most points from DB
• [x] Create new UI model class to expose user ranking fields
• [x] Write a viewmodel with public API to get the top x (50) users of the app
• [x] Write another function to get the current user (potentially with its own UI model class)
• [X] Integrate the viewmodel with the view of #322
• [X] Being able to refresh the leaderboard using pull down on the list

Result

We now have a real leaderboard directly inside the application, which gets populated with real data from the database.
On top of that, we also have a bottom element with our own score and position.

The viewmodel is unit tested in depth and the UI is checked for correctness too.

Note: first relevant commit is 0b29bab.

[gruvw]

Hey, thank you for your feedback, definitely some interesting stuff I missed (like that double wait RTT).