Generic authorship and uncle inclusion module (#2941)

* generalized uncle processing

* add some uncle tests

* set author and do event handling

* OnePerAuthorPerHeight no longer O(n^2) and test

* bump impl_version of node

* Documentation and style fixes

Co-Authored-By: DemiMarie-parity <[email protected]>

* fix #2949: index-based FindAuthor wrapper for srml-session

* use for_each_tuple