Add Spree.t() and missing translations in the en.yml file

I also changed all Spree.t("a_string_word") to Spree.t(:a_string_word)
except for nested ones eg Spring.t("a_nested.string_word")
Correct dependencies
Merge remote-tracking branch 'spree/2-0-stable' into develop

Conflicts:
	app/views/spree/admin/stores/index.html.erb
	app/views/spree/admin/taxonomies/_form.html.erb
Merge remote-tracking branch 'origin/develop' into develop