Fixes #123 -- Add admin actions to send payment reminders and cancelations
Refers #123 -- Add translations
Refers #123 -- Make payment reminder offset configurable
Refers #123 -- Update translations
Refers #123 -- Fix reference to foreign keys
Refers #123 -- Fix translation
Merge pull request #125 from EuroPython/fix/ticket123

Fixes #123 -- Add admin actions to send payment reminders and cancelations