Use stock cupsffi gem.
Update rails and some other gems.
Update CHANGELOG.
Add missing dependency on ffi gem.
Implement support for taxpoint changes and support multiple cantons.

As the current TariffItem/ServiceRecord/Treatment/Session architecture
is less than optimal, this support has been implemented hackish. It
breaks a couple of separation of concerns, but works for now.
Add menu entry for tariff prices.
Add contextual_links to default new template.
Add UI to copy tariff prices.
Update CHANGELOG.
Use #to_s as label method for Person collections.
CHANGELOG.