Add folder popover: Activate on enter

This is expected behavior in dialogs, and makes sense in
this dialog-like popover as well.
App folder dialog: Grab focus to the entry
folder dialog: fix id / name confusion

When creating folders with names that get canonicalized
to a different id, this because a source of crash.

https://bugzilla.gnome.org/show_bug.cgi?id=725976