CommonClient: allow worlds to change title of run_gui without rewriting it

[qwint]

What is this fixing or adding?

moves GameManager to an optional attribute that worlds can update or overwrite as needed

How was this tested?

ran text client with the change, saw no issues,
updated my client to not define run_gui and use self.ui_manager.base_title = "Minit Client" in the init instead and ran it, saw no issues

If this makes graphical changes, please attach screenshots.

[nicholassaylor]

LGTM

[qwint]

updated description to reflect the new design

[qwint]

whoops, didn't notice until i pressed the button that one of those wasn't a treble suggestion lol

[NewSoupVi]

I've reran the unit tests on this branch twice, it refuses to work.

[qwint]

per discussion in core-dev discord channel, changed to a method that returns the kivy App and tested with my own apworld that the following works and i can get rid of my build_gui() override

    def make_gui(self):
        ProxyManager = super().make_gui()
        ProxyManager.base_title = "Minit Client"
        return ProxyManager

[qwint]

to consider: have make_gui return the class instead of an instance of it so if people want to subclass it they can, seemed to work in light testing but have nothing to commit yet

[qwint]

retested new format with the following (and no run_gui)

        ui = super().make_gui()

        class MinitApp(ui):
            base_title = "Minit Client"
        return MinitApp

        ui = super().make_gui()
        ui.base_title = "Minit Client"
        return ui