avatar-convos.png need to change. it's now a picture of me
Add default message if nothing has been said
Add support for convos "system" conversation #16

  - System conversation is available under /convos
  - Will redirect to /convos after wizard
  - Add Core->start_convos_conversation() which will populate the
    convos conversation with welcome messages
  - Add Core::Connection->_add_convos_message which will populate the
    convos conversation with important server messages
  - Improved redirect_last(): Cannot have zero servers
Fix clicking on server messsages in convos message