Nuking the errormsg array was wrong. Continue logging and reporting id.

...but leave the error array in place.
Merge pull request #216 from jbarrett/fix-backtrace-reporting

Fix for reported stack traces.
Move unique ID generation out to DDGC instance.

Get form ID and action token from this function.
Don't set a new action token on check - this effectively makes it per-session.
Breaking screenshot tracking out into a role for use in other contexts.
Rate limiting in the Comment model.