This commit improves the Night Light code in various
ways:
* Turn it into a template class, subclass of GtkDialog,
and adapts all the code to reflect that.
* Update the code style in various places, to make it
more conformant with the documented code style.
* Reorganize the code a bit, moving functions around,
to make it more conformant with the documented order.
This commits adds a new arrangement widget, refactoring the existing
code and addressing a number of issues:
* Forced snapping made laying out more than 2 monitors hard
* Random gaps would be shown between monitors
* The scaling was fixed and usually tiny
https://bugzilla.gnome.org/show_bug.cgi?id=786971
We hard-code a 16x16 asset for sunrise and sunset icons, which makes
them look blurry at higher scaling factors.
Let's look in the icon theme to see if there's an icon for sunrise and
sunset; if not, we can still use the assets we ship, but we also attempt
to load them from different resource paths, depending on the scale
factor.
We will need to update the assets to include a 32x32 rendering of the
sunrise and sunset icons.
https://bugzilla.gnome.org/show_bug.cgi?id=781029
