Change error-handling to be more specific with what it deals with.

I made this change because I'm getting an unreproducable bug in production
which causes duplicate NetInfo, Source, User, Machine, etc objects to be
created.

The old error-handling code just caught all Exceptions. Thus, the duplicate
NetInfo/User/Machine/Action/etc problem we're having could be the result of
some exception other than ObjectDoesNotExist.
Add input to specify sleep time on debug page.
Fix duplicate LogEvents and Errors being created when multiple requests are submitted in quick succession.
Append '?days=0' to the end of all JSON calls that support it.

This is so that later, when someone gets around to adding the buttons
that will make it show stats for just the last week/month/etc,
they'll immediately see how to go about passing the 'days' argument.