CLI interface for minion tasks

- CLI_Command class is invoked from index.php to run Tasks

- Task factory takes a $name, and is executed with $params
  - CLI_Command::factory($task)->execute($params);

- Interfaces for standard I/O 
  - CLI_Input
    -  read()
    -  options()
  - CLI_Output
    - write()
    - writeln()
  - CLI_Options
    - Handles Task selection and params collection

- Backwards-compatible with 3.3 Task interface


I tested the upgrade with an existing production application which contains several dozen tasks. All of the tasks ran correctly. Much more unit testing is needed in this module, as even before this PR it only had one test. We should add more to the branch as we go along.