JCLOUDS-67: Filtered license headers from script fragments

Filtered the license headers in script fragments, to avoid having them repeated when composing scripts.

To avoid modifying the different existing function loaders, added a decorator in the CurrentFunctionLoader class that performs the filtering on the returned loader.

**On the commits in this PR:** This PR is rebased to the latest version of the ASF/master branch, but when sending the PR two commits from Adrian appeared. Is the sync process working or is it something missing in the mirror?

/cc @adriancole