Bug 705403 — Use GLib.BytesIcon instead of Edsf.MemoryIcon

Use GLib.BytesIcon internally instead of Edsf.MemoryIcon, which can
be deleted. This bumps our GLib requirement to 2.37.6, but doesn’t
affect API.

Closes: https://bugzilla.gnome.org/show_bug.cgi?id=705403