Refactor update_io_button

Refactor update_io_button

Check, in order, if the io is connected to another Ardour route, then a
user bundle, then some physical ports with simple configuration, and
lastly another client.

Before, Routes were considered connected as long as every io port
connected to that route, even if the channel order was mixed or worse if
all ports were connected to the same channel. Now Routes and Bundles are
considered connected if they are exclusively connected, in the right
order, to all their ports with matching datatype.