Log message:
devel: Add libdazzle.

Needed for epiphany update.

The libdazzle library is a companion library to GObject and Gtk+. It provides
various features that we wish were in the underlying library but cannot for
various reasons. In most cases, they are wildly out of scope for those
libraries. In other cases, our design isn't quite generic enough to work
for everyone.

The libdazzle project is heavily opinionated, and tends to gravitate towards
design that matches the GNOME 3 human interface guidelines.