Copy/Move File Prompt #13

To me, it feels more natural to allow a user to drag any supported media file to the app window to include it in the project, rather than only files that have already been added to the project folder. When a user drags a supported media file to the window it should:

1. Seamlessly fall into the project if already included in the project folder.
2. Prompt a system dialogue asking the user if they would like to copy OR move the file if it is not already in the project folder.
3. Provide an error message dialogue to the user if the file is not a supported media type.