Catch exceptions in version display template tags
Catch exceptions in version display template tags

According to the Django documentation, exceptions raised from a template
tags or filter will be exposed as a server error. To avoid this, the
version template tag now returns "unknown", if an exception is raised.

fzadow/CATMAID,fzadow/CATMAID,fzadow/CATMAID,fzadow/CATMAID