Report status for infrastructure ASes and APs

[matzf]

For a broken attachment points, the display name was changed to "do NOT use [was WISC]" to indicate that this attachment point is permanently down. Rather clumsy.

Add functionality to track the status of the scionlab infrastructure. On the admin panel, we should be able to mark an AS as temporarily or permanently down, with a message explaining the circumstances to admins and to the public.
Report issues with the infrastructure on the main scionlab page. Report issues with APs for affected user ASes on the user-AS overview page. Disable affected AP from drop down list.

[matzf]

Related: #149

[mkowalski]

https://github.com/CachetHQ/Cachet could be used to provide with the status and stuff like this. People should be somehow familiar with this, as it's being already used by lots of projects/entities.