Combine the search bar and query editor

This is the adaptation of Nautilus commit 5521f24f74d18bad5cbec893f4cf42503fe8d02b

Original commit message:
Save vertical space by integrating the search bar
with the query editor. This makes it less visually
disruptive when a search becomes active.

https://bugzilla.gnome.org/show_bug.cgi?id=679900