Fix a wrong constant in tests
Use a separate file for route filters
Do not use unnecessary REQUEST_BASE_URL ('/')
Configure I18n inside 'configure' block

(I do not know if this changes anything.)
Move some private methods from public to init
Comment out unused methods
Use a new helper 'fixed_url_with_locale'
Format
Work on hidden_fields_from_nested_hash helper
Add a helper for url queries from nested hashs
Move filtering participants in index to a method

An ugly solution to make the index action for participants more readable.
Allow downloading filtered participants as CSV