Include group titles in search

When searching for messages only simple threads matching the contact
names are returned as search results. With this commit also group
converstations where the group title matches the search term are
displayed in the result. This makes search results more consistent with the
conversation list as now all conversation titles (i.e. contact names and
group titles) are searched through.

Fixes #1954
Yeah, I had to do this with the fuzzy filter in ContactsDatabase. The param string needs the "%"s as far as I was able to tell.