tag is now a cassandra model
setup cql create for tag
bin as a python module
create default tags in User.create method
no more static tags, use of user.tags property
rename external_thread id to external_parent_id
fix a bit tag expand, need more attention later
don't forget real address from a mail, so use a Recipient object to store contact and real address
fix use of Recipient instead of only Contact
do not generate static random tags, use of user.tags instead
security_level stored in cassandra message and thread, update thread with min value found
use of cornice.resource instead of simple pyramid view
UserMessage.recipients instead of contact, and ensure to index address not only contact_id