Added Sync menu with check-box option for enabling or disabling
automatic synchronization.  Note this is just the view portion, no actual 
syncing currently takes place.
Added get_filename method to results writer classes.
WorkUnits' callback now passes the full path to the output results file
rather than the the input filename.  WorkUnits are now passed the output
context in their constructor in order to provide this information.
Added SynchronizationManager class which keeps track of files to be 
synchronized and creates threads which copy them to VOSpace when
syncing is enabled.
Added is_remote method to WorkingContexts.
UIModel is now passed a synchronization manager in its constructor.
Hooked up synchronization manager in model to view and controller.
Disable the sync menu if we are working locally.
Merge pull request #118 from drusk/autosync

Closes #104.