Templating helpers

Added the following helpers:
- possify: transforms "Jakob" to "Jakob's" or "Jakobs", depending on language)
- inWater: transforms "Mälaren" to "i Mälaren" or "in Mälaren" or empty string, if there is no water)
- catchTitle: transforms a json of catch-data to a string of name, weight and length, according to metric or imperial system, depending on user settings)