Move license header before package declaration in all *.java files

In LUCENE-7012 we committed a change to the IDE templates to place the license header before the package declaration in new Java files.

I wrote a simple Python script which moves the header before the package declaration. To be on the safe side, if a .java file does not already start with the license header or with package org.apache, it doesn't modify it and asks for manual intervention.

It runs quite fast, so I don't mind running and committing one module at a time.