This is mostly a simple lexical search+replace but the absence of operator< for
std::weak_ptr<T> leads to some complications, particularly with Evoral::Sequence
and ExportPortChannel.
Copyright-holder and year information is extracted from git log.
git history begins in 2005. So (C) from 1998..2005 is lost. Also some
(C) assignment of commits where the committer didn't use --author.
Remove Canvas::Layout, use Canvas::Container for the same purpose, move child-rendering into Item::render_children() so that it
could theoretically be used by any derived type.
