Fixes and Features #2

Sound:
Added locks around disposal so that hopefully it will now be thread safe (more testing needed to confirm)
Made Refresh Properties update according to the parent Cue
Tweaked some Reimport code (added dialog filter etc)

Cue:
Updated the RefreshProperties to accept the cue passing to the Sound for updating vars based on the cue

MainWindowVM:
Adjusted Open Document so that if you cancel it doesn't add a null to the Documents list
Added CanExecute method for Reimports (can no longer call reimport on empty Doc)
Reimports now Only will fire if you have a Sound Selected (for Reimport Selected and Reimport Selected from new Location)
Added dialog filter
Message boxes saying that the file name is different now tell you what file you are trying to import vs the one that you have selected

SoundView:
Cleaned up the SoundView so it's easier to maintain in the future
Added "File Last Modified : " line so you can see what version you have loaded currently. Should make easier to see if you have an old version