Add color coding to Versions and Repositores tables

[AMDmi3]

For tables which are sorted by repository (e.g. project Versions page and Repositories list), it would make sense to (at least experiment with) make use of color values associated with repositories and introduce color coding for easier visual navigation. It may be in a form of extra column (very thin, near the Repository column) filled by associated color, a colored bullet near the repository name (similar to medals in sorted Repositories), or colored row background (need to process a color to make it lighter and less saturated).

This would require a dedicated endpoint serving .css which provides repository-specific styles (and we should be careful with its caching).