Update testing gems

Apparently Mocha needed to be updated for updated Rails.
Clean up list#prepare_content, #handle_send_action

Just trying to make it legible. Prepping to get message length limit.
Calculate message max length (including prefix/suffix) for web message

- Still need to do this for welcome message
- Would be nice if web messages came from a number
MessagesController should get_list scoped by organization

Otherwise anybody could send to any list, theoretically