repo get - "clean" parameter support

[szymon-owczarzak]

In my project we are using repo script for creating our demo/test content package.

We often prepare content on local author instance and then use ./repo get -f <content_path> and then we commit the content in the repository. However repo get will checkout all the properties even those that are not need (not desirable) like jcr:created, jcr:createdBy etc.

Cleaning process before commit is tedious that is why we have updated version of repo script that removes those props when you use new -c parameter.

I could prepare PR with such change to repo script if this is something desirable. Please let me know.