Use zone information from API

[PeterJCLaw]

The number of the zones and arrangement of the colours within the arena is not guaranteed to be fixed. It is defined as part of the compstate and is available via the API, through the corners endpoints.

Currently the livestream overlay seems to have these hardcoded, which means it's liable to be wrong if the corners colours ever change. (In the past this has happened due to accidental mislabelling of the arena corners; srcomp's support for this is intentional to cope with that scenario).