BUG: 0001832 0003140 0003209 avoid crashes by catching exceptions

Some libraries and systems throw exceptions, but Qt's default
event processing does not catch them[1]. For example, slicer
could crash when ctkDICOMItem is pointed to a file that does
not exist. Wrapping event processing in try/catch should handle
other conditions, like out of memory exceptions thrown from
inside render operations (e.g. due to overly complex glyph
rendering).

[1] http://qt-project.org/doc/qt-4.8/exceptionsafety.html

http://stackoverflow.com/questions/10665655/how-to-log-uncatched-exceptions-of-a-qapplication

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22273 3bd1e089-480b-0410-8dfb-8563597acbee