Modification of error reports database

[jhaigh0]

As part of the error reporting overhaul Epic, the ErrorReport model will need to be modified to facilitate the linking of error reports to github issues. At the simplest level, this will mean adding an issue number field. Since there will be duplicate reports of the same bug, it may make sense to normalise the models by creating an issue model (similar to the user info model) which holds the issue number and a comparable version of the stack trace.