Rewrite the comments to be more understandable, remove some sharp edges like the need to clean build directory, and format the expression.

appstream-glib modernized its validation (https://github.com/hughsie/appstream-glib/commit/2eb9b8caf9ca22ac914b63f34fea5dd6da6f4e76)
making appstream-util complain about these:

	• tag-missing           : <content_rating> required [use https://odrs.gnome.org/oars]
	• tag-missing           : <release> required

I fixed the first one by using empty content rating tag like Epiphany does,
and the second one by wrapping all the releases in releases tag.

Unfortunately, that revealed more issues:

	• attribute-missing     : <release> has no timestamp
	• style-invalid         : <p> is too short [Added 28 new comics, including:]

The first one caused by us including an unreleased release, the second one is just super weird,
since there are even shorter paragraphs before some lists.

I decided to resign and use validate-relax.

Bind show statusbar and toolbar GSettings values directly to GAction.

https://developer.gnome.org/gtk3/stable/checklist-modifiers.html

GTK+ only calls `setlocale (LC_ALL, "")`, not any other gettext calls.

- store cache files to $XDG_CACHE_HOME/buoh
- store configuration to $XDG_CONFIG_HOME/buoh
- if the legacy $HOME/.buoh exists, use that for configuration

No migration step was added, users will need to migrate manually
if they want to.

Balló György authored Dec 20, 2014 and Jan Tojnar committed Jan 23, 2019

- Don't disable scrollbars, otherwise the window cannot be resized
- Set the default size of main window

https://bugzilla.gnome.org/show_bug.cgi?id=741798

https://wiki.gnome.org/Initiatives/GnomeGoals/AppDataGnomeSoftware

also stop using GtkUiManager