Review and improve expectations around corner numbering and ordering

[PeterJCLaw]

Following from PeterJCLaw/srcomp#27 it seems that this repo relies on the ordering of the keys in the mapping returned from /corners is the same as the order of the list of teams in a match. This appears to currently work, however this is due to us always naming corners 0, 1, 2 and 3 in that order.

It is unclear whether this is something that should be relied upon -- specifically whether JSON & JavaScript mappings' keys have defined stable orderings.