Convert tool bars to QAction

Convert I/O tool bar buttons to QActions's, and a QToolBar (rather than
QHBoxLayout) to hold them, which gives us auto-raise and text style for
lower cost (besides that they really should be QAction's anyway). DO
likewise with the navigation tool bar, and also remove the hooks to not
add the actions.
Add search options menu

Add an option menu to the navigation tool bar. For now it is empty
(except things services add), but will soon have some common options
also.
Add option to include saved results

Add a search option to include in search results items which have
already been saved to the archive. Note that this depends on the service
implementation to actually request loading from the archive when it
detects that a result is already in the database. (Probably this should
be refactored to move more of this code to the base Service, but not
doing that now...)
Fix scaling of result thumbnails

Explicitly resize result thumbnails to fit into the desired size, if
larger. This is supposed to be handled by QAbstractItemView.iconSize,
but for some reason doesn't seem to be working. Also it's much more
strongly desirable for memory usage when we're generating thumbnails
from full-sized saved results (to not keep the full result image in
memory), which wasn't as important for result thumbnails off the web
that were at most a little bit larger than desired size.