Merge branch 'sev/menu_charmap' into 'master'

Improved playername charmap

The current playername charmap is of quite a low quality:
- It uses a low-resolution, pre-rendered image of the characters
- The arrangement of the characters is random and redundant

This branch reimplements the charmap:
- The characters are defined in the qc sourcefile and rendered in-game
- They are arranged in a more logical way
- I've added the new Unicode dingbats from the Xolonium font (currently requires checkout of branch sev/xolonium in the main xonotic repo)

![charmap](https://gitlab.com/uploads/xonotic/xonotic-data.pk3dir/ce6d73410d/charmap.png)

For maintainability, I would prefer to directly include the UTF-8 encoded characters in the sourcefile, instead of the hex value, e.g. strzone("★").
But I first wanted to ask for your policy/opinion about including non-ASCII characters.

See merge request !60