Add a t-shirt color to team object

[kunyavskiy]

It's availiable on finals, we use it in live to make a coloring of team-related things (like achivements and solved problems when team is shown).

Note: maybe also adding text color make sense, but we don't use it right now..

[deboer-tim]

For most new properties we start by adding an extended (non-spec) property and use it in a couple contests, to prove that it's useful (to more than one tool) and get some feedback. These are allowed by the spec and here are some examples from the CDS: https://github.com/icpctools/icpctools/blob/main/doc/spec-extensions.md. Some stay tool-specific forever, some get adopted directly, others take time or we find a different way to add to the spec. The main point is that we try not to add things that are theoretically useful, we try it out with one or two teams and then formalize it for others.

Does the current t-shirt colour come from the CMS? If so we should start by asking them to include it as a property in the export. This is the key thing that needs to be done, and we can start using it immediately. If you open an issue on the ICPC Tools repo we can easily add CDS support. The property name doesn't really matter, but I'd suggest team 'rgb' or 'color' to match problems (and not specific to t-shirts) and make it more likely to be adopted in the spec without change later.

[kunyavskiy]

It comes from cms. Unfortunately, Lidia claims data is not very accurate (as it corresponds to colors requested, not ones actualy printed). So I'm not sure how useful this export would be.