Update to understand maintenance mode (purple)

When the tree is closed for maintenace the status goes purple.

Reflect this with red & yellow - red but likely to go green without developer intervention.
Oops - disambiguate Red/Yellow

This uses Red+Green as the common error for uninterperable tree,
but adds flashing amber as - Can't read status, which overlaps nicely with flashing amber - Can't connect to network.
Merge pull request #3 from petermayo/patch-1

Update to understand maintenance mode (purple)