FetchCord GUI Bug Fixes

[TabulateJarl8]

I was testing the FetchCord GUI when I was bored today, and I fixed a few bugs.

• Fixed bug where arguments weren't being interpreted (shell=True in subprocess call was breaking arguments)
• Fixed bug where user could type in anything for the terminal name; user now has a selection of the available terminal names (L40-L43)
• GUI will now detect running fetchcord processes when started, preventing the user from starting a new one until the "Stop" button is pressed. (uses psutil to create a Process object of the process in question)