placessidebar: add Other Locations item

placessidebar: add Other Locations item

Places sidebar is a widget that enabled the user to select
XDG directories, bookmarks and mounted network locations,
as well as manages permanent and removable devices.

The new design that aims to look less clutered makes the
sidebar display only removable devices, as well as mounted
networks, bookmarks and XDG directories, and delegates the
management of permanent devices such as hard drive partitions
to GtkPlacesView, a newly introduced widget for this specific
purpose.

To delegate it, add an "Other Locations..." item to notify
when the permanent devices manager is required. Besides that,
don't show these fixes devices on the sidebar itself, as they
are not supposed to be handled by the sidebar anymore.

https://bugzilla.gnome.org/show_bug.cgi?id=752034