To prepare for translation support, this makes all of the widgets
cognizant of the language change event that occurs whenever
installTranslator() is called and automatically retranslates their text
where necessary.

This is important as calling the backing UI's retranslateUi() is often
not enough, particularly in cases where we add our own strings that
aren't controlled by it. In that case we need to manually refresh the
strings ourselves.

1. This is something that should be solely emitted by the hotkey dialog
itself
2. This is functionally unused, given there's nothing listening for the
signal.

Avoids a -Wreorder compiler warning.

* Adds a new Hotkeys tab in the Controls group.
* Double-click a Hotkey to rebind it.

Instead, we make a proper registry class and house it within the main
window, then pass it to whatever needs access to the loaded hotkeys.

This way, we avoid a global variable, and don't need to initialize a
std::map instance before the program can do anything.

Makes code consistent with our style of defaulting special member
functions where applicable.

Allows users to choose a single screen layout or a large screen layout.
Adds a configuration option to change the prominent screen.

This makes clang-format useful on those.

Also add a bunch of forgotten transitive includes, which otherwise
prevented compilation.