Refactor library_browse
library_browse should store the height of the view

Fixes a change from 7a33ea8 (part of the port to pygobject).
Remove leftover from '..' and '/'

This was previously used to avoid saving those special rows as the selection.
library_populate_toplevel_data only takes view

Also hits library_get_toplevel_cache, a companion.

It is simpler to pass just the view, as the views can't overlap for
toplevel data.