Move graphing logic to Graph module #129
Description
Currently, when the user clicks on the Plot Data button in the GUI, an Observable global value in the vdisp module (I plan on moving these variables to their own module, so they may appear somewhere else by the time this issue is addressed) called graphData is set to true. This Observable type has a Listener function attached to it that executes the graphing functionality every time graphData is set to true. This logic should be moved to one or more functions in its own module, probably called Graph.jl, and these functions are what should be called from the Listener.