Threading and Buttons

Added a new thread for DownloadFile, so the program doesn't become
unresponsive while while downloading.
Added functionality to the Download and Upload song menu items.
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Currently, the server cannot open the file, and therefore will not send
the file to the client. Can someone look into this?
Finally, we still need the server to open a new socket for the
downloading and uploading.
Fixed Bug

Small bug I introduced where the client would send bad data to the
server. Fixed the issue. However, the server issue from my previous post
remains.