Combine the three toolbars into one

[cbrnr]

I don't see the need for three separate toolbars. Therefore, I suggest to combine them into one toolbar and add separators to group icons accordingly.

[Yida-Lin]

@cbrnr Hmmmmm.

Not sure whether this is necessary, since I sense this would involve some significant changes. However, if I were to do it, I would really wish to add a designer form for the main window for more intuitive control. Also easier to add more buttons etc., such as the one "auto-center"

[cbrnr]

I'm working on that one, it's not that complicated even without Designer.