Corrected translation references in templates

Were using old entity naming scheme (*.ss) instead
of underscored version which doesn't create a new YML
namespace. This means all existing translations should indeed be used.
Was already fixed in master, but not in 3.1
More mappings for i18n::tinymce_lang
Behat test for language switching
Updated translations
Added 3.1.1 changelog
Updated translations
Added 3.1.1 changelog
Merge remote-tracking branch 'origin/tmp-3.1.0' into 3.1

Conflicts:
	docs/en/changelogs/3.1.1.md
	tests/behat/features/profile.feature