make sure every popup has a parent JFrame

[sadraskol]

this PR solves #111 Popups should have a parent specified to be opened relatively to the parent's frame. As stated in the documentation (https://docs.oracle.com/javase/8/docs/api/javax/swing/JOptionPane.html#createDialog-java.awt.Component-java.lang.String-)

As a result, I had to pass the parent in chains of static calls. That doesn't feel right, but I couldn't find another way to writing it that didn't change the current structure of files.

:chicken: Things to fix still:

• [x] I don't understand how eclipse formatting work, so SimpleGui is a mess
• [ ] I haven't commented the code, I don't know exactly what and where I should specify the role of the "parent"

[pkriens]

Thanks for the work. I agree that the static nature of Alloy is bad engineering, although I find this all too common in our industry. We are taught that global variables are bad but somehow statics seem to escape scrutiny. And they really suck if you want to reuse code.