Improved search experience: Bug #720361

This introduces a new full-text search algorithm that attempts to
curb the effects of overstemming in the Porter Snowball stemmer.
The FTS table will be regenerated with this update.

The crux of this new algorithm is a configurable heuristic that
reduces stemmed matching.  The configuration is not available via the
UI (I suspect it will only confuse users) but can be changed by power
users via GSettings.  More information is available at:

https://wiki.gnome.org/Apps/Geary/FullTextSearchStrategy