Only show one system status with >1 incidents.

[dracos]

This stops the duplication of/incorrect system statuses when there are multiple active incidents. It works out the maximum level to display. Fixes #32.

I don't really know Hugo at all, but I couldn't see any way to do this without having both ways of the levels lookup. This does work, but hopefully you might know a nicer way!

[steveoh]

I'd love this to get a nice review and merged if it's solid @verythorough

[steveoh]

☎️