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.
* Update button when the name of a connected route changes
* Indicate partial internal connections (previously only the
client name ("ardour") was displayed.
* Escape markup in I/O plugin and client names
* Refactor code, use a common base-class for route and
route-less I/O Buttons
