New feature: auto-completion for the location bar

I implemented auto-completion for the location bar.

Persistent storage of the browsing history (URI's and titles) is not implemented yet because i haven't decided on the format we should use for storing the history. There's a bookmarks file parser API in GLib but the file format has a lot of overhead (XML...). I haven't really done any serious research on that topic, though. What do you think?

Link: https://developer.gnome.org/glib/stable/glib-Bookmark-file-parser.html