New recipes datomic::download and datomic::console

This PR generalizes the cookbook to provide 2 new recipes:
* datomic::download downloads and unpacks a Datomic distribution; this is sufficient to run [Datomic Shell](http://docs.datomic.com/shell.html) and/or [Datomic backups](http://docs.datomic.com/backup.html).
* datomic::console installs a running [Datomic Console](http://docs.datomic.com/console.html) service using bluepill