global: fix copyright notice years

• Every file has a copyright notice where the year information was sometimes invalid (starting always at 2002 instead of at the actual year when the concrete file started). This commit fixes this pre-dating problem by deducing copyright years from the source code commit history. (closes #172)

• Note that this solution is not fully ideal either, because some files were renamed in the past -- especially when we have been using CVS and later CVS-to-Git migration -- therefore we may be missing out on some early 2002-2003 years because we took only the current file name commit history into account in this fix.