MacGui: Activity Window Logging Initial Implementation

MacGui: Activity Window Logging Initial Implementation
- stderr and stdout are now written to a .txt file as well as displayed in the activity window
- Each line from stdout and stderr is written as it comes out of libhb (instead of in batches) so that in the event of a crash, we see the very last log message just like in the cli output
- Log file is located at: ~/Library/Application Support/HandBrake/HandBrake-activitylog.txt
- Uses .txt file as .log files default to open in console (text editor is more user friendly to n00bs?).
- For initial implementation, log file is overwritten for each session, and the current date and time is printed at the top of the log. So, log is one session long, for now.
- Activity window is also now a normal window (not an inspector) so that you can minimize it and the picture preview window is not half covered up by it on a smaller (mbp) display
- Added "Open Log File" to the Activity Window contextual menu which opens the log file in the users default text editor

git-svn-id: svn://localhost/HandBrake/trunk@1058 b64f7644-9d1e-0410-96f1-a4d463321fa5