Also removes the return value from the BITMAP_STORE's themeChanged
method as it will provide the wrong answer for the second frame it's
called on.
Also hooked up ACTION_TOOLBAR, the app launcher, and the project tree
to the wx event for system color changes so they change on the fly.
Fixes https://gitlab.com/kicad/code/kicad/issues/6026
This allows us to avoid the monospaced font (along with the tab-stop
handling), and process a <return> as an OK rather than just <shift> +
<return>.
Fixes https://gitlab.com/kicad/code/kicad/issues/8425