Advise user of fixed bugs when error occurs

[Tom Goddard]

Would be nice if our error dialog could check if the traceback signature matches a known fixed bug and say in the error dialog "This bug was reported Nov 25, 2018 and was fixed Nov 29, 2018. Get the ChimeraX daily build.".

The way I envision this working is that a signature computed from the traceback stripping off the Python file paths to just the location of the .py files in site-packages and including line numbers would need to exactly match a traceback from a fixed Trac ticket. A script would daily run over our Trac tickets and extract these traceback signatures and put them in a file that ChimeraX would fetch when a user tries to report a bug. That file could be cached locally for use when the next error occurs to avoid a delay from the server. Alternatively a query to our server could search for info on this bug in the file and report back.

The advantages of this:

1) User's get faster feedback about how to fix their problem.
2) We don't waste time handling duplicate bug reports.
3) User's see that we fix bugs promptly, so are more inclined to report them.l