Some tweaks to the appearance

Change the main view to use a header bar, and make the search
entry appear as in the design. Some not-fleshed out interactive
pieces have been removed from the ui file for now. They can
come back later.

https://bugzilla.gnome.org/show_bug.cgi?id=706049
Rename button_new to button_all

The label is 'All', so it makes more sense to call it this.

https://bugzilla.gnome.org/show_bug.cgi?id=706049