Better handle multiple identical alerts

[justin-bits]

Current alert de-duplication doesn't kick in until ~five alerts. Having multiple identical alerts cover up 20% of the application as they run up the page isn't more helpful than just being notified once. It also causes problems with automated tests in unstable environments.

Find a way to fold these up, notifying the user that the issue occurred multiple times. As an example, duplicate console errors in Chrome (and probably Firefox) can be nicely collapsed with a badge that indicates how many times the error occurred. The relevant information is still displayed without the visual spam.