skeleton of packageAst as a task

TODO:
- Figure out if using Package.makeJar is a good option
  - If yes, where can we get the Logger to use?
  - If yes, what is exactly the mapping (File, String) ?
  - If yes, how to create a proper Manifest?
. Figure out how to get current config in task
- Other possibility: do everything "as I want, i.e. without
respecting SBT config system for packaging.