Doc: all: clarify licensing and copyrights

This clarifies that documentation is under CC-BY-SA v4.0+, and assigns the
proper original copyright year to each generated document (rather than mark
them all as 2009). The Pacemaker Development FAQ has been updated accordingly.

This also moves the text of actual licenses to a new licenses subdirectory,
and the COPYING file now says which license applies to which files.
The spec file has been updated accordingly.