This helps isolate the inspector from some of the changes that
it can trigger. To specify a different display, set
GTK_INSPECTOR_DISPLAY to the name of the display to use for
the inspector window. If no display is specified, GTK+ will
use a separate connection to the default display.
Move the touchscreen switch to the other debug switches, and
move the hidpi spin to the other graphical controls. Since the
Visual tab is getting large, make it scroll. The General tab
is purely informational again.
Some of the features we expose can be hardcoded via environment
variables. In that case, don't confuse the user by letting them
change settings that have no effect.
The entire UI is constructed with templates, so the wrapper
constructors are never called, except for gtk_inspector_window_new,
which gets called from the GTK+ code.
