mainToolbar: Remove useless signal connections

We do not use SearchMatchManager or SourceManager or anything inside
them while setting the title. Hence there is no need to listen for the
active search match or source.

https://bugzilla.gnome.org/show_bug.cgi?id=686461
application: Prioritize relevant rdf:types

https://bugzilla.gnome.org/show_bug.cgi?id=726796
documents: Make the emblem rendering robust against theme failures

Fallout from 54aa0abb6f10bf3dc3068918bcc96128d1a45433

https://bugzilla.gnome.org/show_bug.cgi?id=726885
documents: Skip icon-less documents for collection icons and effects

This can happen if we failed to load the icon based on the MIME or
RDF type. A very unlikely possibility, but no harm in being robust
against it.

https://bugzilla.gnome.org/show_bug.cgi?id=726885