Refactoring:
* maven-style publishing;
* restructured ami classes:
  + separated parts of the userscript;
  + made an abstract `AmazonLinuxAMI` class and an instance of it for a particular version of ami;
  + made tags optional;
  + removed (useless) AMI bundle, DummyDistribution and related test;
* changes in the userscript (applicator):
  + updated to sbt 0.13.0;
  + updated to sbt-s3-resolver 0.6.0;
  + removed dependencies on statika and bundle (now only distribution);
  + removed tagging from the applicator;