Status page bug fixes

[alycejenni]

• cache iiif status response for 300s
• timeout response after 5s
• add helper to check if route exists
• use helper to check if status.index exists before using it

[jrdh]

Presumably the maxsize=1024 here is just an arbitary number given there's no arguments on the function so there will always only ever be 1 item in the cache? Doesn't need to be changed or anything, just checking my understanding is correct.

Also, unless I'm misunderstanding how cachetools implements a TTL cache, this will cache the function result for 5 mins but that 5 mins TTL will be reset each time the function is called. So if we still tie calling this function to page requests and we consistently get at least 1 page request every 5 mins, the status will never be updated as the cached copy will live forever?

[alycejenni]

maxsize is probably unnecessary, I'll remove it.
The TTL doesn't get reset every time it's requested so it should be fine (confirmed by me testing and you going through the code)

[coveralls]

coverage: 33.017% (+0.001%) from 33.016%
when pulling 28994d3 on ginger/status-bugs
into 3c3b247 on dev.