#27229 Added logging to file and better exception traps.

- Engine log channels are now trapped in /usr/discreet/log/tk-flame.log
  via a standard python logger. 
- The exception trap has been extended to send to the log file and
  has been moved into the main engine. This means that whenever there
  is a QApplication running and an uncaught exception is being raised,
  a messagebox is being displayed.