PE7 WIP code

It only pops up the GUI, but the last part SHOULD be pretty straightforward. I copied over the prime finder from PE3 and it sits in a separate .c file. I'm glad I was able to combine my two learning projects: GTK and PE.

EDIT: I don't think it will be long before I'm going to force myself to learn Glade so that I don't have to code the GUI by hand. That was super tedious and there are only six widgets involved!

So the typedef for the struct is because in my callback function I needed to initialize a pointer to the widget data structure to the gpointer passed to the function. Just saying "struct Widgets *widgets" wasn't working so then I put in the typedef part. THEN I learned that a type defined in main doesn't carry over to functions that main calls so I tossed it outside of main. I don't know if making it typedef or putting it outside of main is what let me define a pointer to it but it doesn't matter. I'm really close to putting it into a header file to clean things up a bit.