Grand scale UI rewrite using GtkBuilder

Rationale

There is no real rationale behind this except that Glade should be able to demonstrate the use of itself, all the Glade interfaces should be written with use of GtkBuilder to the max, and then Glade should install Glade files for all of its components separately.

The only reason why we havent done this before is because of namespace complications, making it difficult and tiresome to try to link to the libglade library inside the Glade application.

This is more of an interesting excersize for a beginner and a nice to have long term goal than an important roadmap item.