The get_factory_context becomes 'public'

Removed the leading underscore in the name of the method, to be
considered as 'public' instead of 'protected'
Added a "samples" folder, with some sample code

- The "samples" folder is a Python package that will contain some
  examples to use service from or to develop extensions for Pelix/iPOPO
- The first sample is the implementation of a "logger" iPOPO handler
  which injects a logger in the given field of the component