Add achievements tab to score window

[jbytheway]

Summary

SUMMARY: Interface "Add achievements tab to score window"

Purpose of change

Players should to be able to see the new achievements feature, and their progress towards achievements.

Describe the solution

Add a new tab to the scores UI. I made it the first tab, because I hope it will soon be the most interesting.

It's fairly simple, it simply lists each achievement together with its requirements. They are coloured according to their status.

Testing

Looking at the window in-game, and a small unit test.

Additional context

When pending:

When complete:

Some features aren't obvious here:

• Each requirement is coloured independently.
• The incomplete achievements are all sorted before the complete ones, but then sorted by translated description within that. Longer term, I plan to permit each achievement to have a sort key in json to control its sort order, so that similar achievements can appear together.