Changes `libraryTreeView::addEventListener('load')` and similar to
`libraryTreeView::onLoad.addListener(listener, once)`, etc. `once` is an
optional boolean that, when true, causes the listener to fire once and
then be removed. This is implicit for 'load'.
'load' maintains its special behavior of running immediately if the
treeview has already been loaded.
Also adds `waitForLoad()` and `waitForSelect()` functions that return
promises on event completion, since most uses of those events were just
resolving deferreds.
With icons to identify collections and searches
Also:
- `savedSearch` search condition in general
- Clean up some search window code
- Reorganize search tests
