ENH: Allow expInfo fields to be marked as required (*)

[ainazay]

This is the qtgui.py file, updated with a new function called "validate," in response to the issue:

#4412

[TEParsons]

I can see what you were trying to do with validate but from the looks of it the function was never called and contained some references to attributes which didn't exist. I've pushed some changes which implement a similar idea, hope that's okay!