certs - changed the logic of free/paid certs to be limited/unlimited.
no auto update - migrate the couch before
restrict couch access to admin
make sure couchrest actually finds our models in the engines
create sessions db - it's not a CouchRest Model db.
setup user and restrict db access
simulate couch migration workflow on travis

* first setup couch similar to what we'll have on the platform
* then run migrations as admin
* then drop admin privileges
* then proceed with the normal test script
updated deploy documentation

INSTALL is mostly for development and we do not include couch security advices in there
Merge pull request #37 from azul/feature/migration-flow

Migration flow for couch db
Merge branch 'master' into feature/billing