pledge_domains() that takes only one String argument was specifically
added as a shortcut for pledging a single domain. So, it makes sense to
use singular here.
In order to propagate errors that occur during UI setup, we have to move
all that logic out of widget/window subclass constructors. This is a
first attempt at doing that, for GUI::SettingsWindow.
The settings for Terminal are extracted into their own application,
TerminalSettings, which is reachable over the normal Settings menu as
well as the same place in the Terminal menu. The font settings are moved
into these settings as well, which are now split up into the "Terminal"
and "View" tabs. The font settings themselves receive an option to
override the selected font with the system default on the user side.
The live update behavior of all of the terminal settings is retained.
The layout of the new TerminalSettings is based around the other
Settings applications, but pixel-perfectness is missing in some places.
It's a bit fiddly and I'd like to have some better GUI::Label auto-size
behavior, but oh well :^)
