Add ability to redefine orientation of incoming/outgoing connection for a specific anchor.

[ma-efremoff]

At the moment all connections are oriented in the same way, horizontally or vertically.
But in some cases it is required to redefine the behaviour of a specific connection, especially for anchors.

Please provide ability to make timer -> join, join -> timer connections vertically oriented.

[draedful]

Developer Notes

We recently introduced a new concept of ports - #128. It seems that these ports can and should have some knowledge of which way connections can go (after all, they were created for connections, and there is no other reason to create them). So I think it makes sense to consider extending the interface with a new field `direction: top | left | bottom | right'.
And already the connections will be able to look at this field and use it to build connections.