add an updatestatus on the index page

[rschrieken]

queries sys.database so might need extra scrutiny for performance before merged because this get called for every fetch on /Index, basically the homepage.

This fixes: https://meta.stackexchange.com/questions/315014/improvements-to-data-updated-x-hours-days-ago-message-in-sede

[NickCraver]

We should collapse this into a multi-query if attempting it, but I'm not sure the app actually has permissions to see the _Temp database while restoring anyway. That's a question for @tarynpratt :)