GUI redesign - Part 2

Second and last part of the GUI redesign. Plenty of changes to go around, I can't even list them all, but here are the most important:
- New recommended mods dialog
- New dialog for TooMuchProvidesKraken situations
- Apply button no longer exists, along with the issues associated with it

@pjf - feel free to make a new release if everything is ok with the PR :)

Closes #404 
Closes #348 
Closes #300 
Closes #139 
When I was learning C# I never realised structs couldn't have default values. Thank you for doing this.