Create en language on db:seed and update action_kit:import_languages

[rodrei]

Proposed solution:

• Make field actinkit_uri optional.
• Create en language on db:seed
• action_kit:import_languages should delete all existing languages and then import the ones in AK (import already implemented)
• [minor] When creating a language, language code can't be uppercase. Perhaps downcase before saving? If you create a language with an uppercase code, e.g. EN, champaign dies.