Bug 720335
* src/client/composer/spell-check-popover.vala
Implemented a GtkPopover allowing the user to select a
subset of the currently installed dictionaries for the spell
checking in the composer widget.
* src/client/util/util-international-vala
Added detection of installed dictionaries and proper
translation of the available languages. This requires
Enchant as an additional dependency.
* src/client/application/geary-config.vala
Added keys spell-check-visible-languages and
spell-check-languages in GSettings.
