Support portage tag on canoe view

[quincylvania]

Once again, love the tool!

Right now the tool supports canoe=portage on the canoe view to connect waterways over land. Lately I've been using the more robust tag portage=* on these ways to better distinguish different access scenarios. I propose supporting ways with positive portage values as part of the paddle network, and excluding negative portage values.

The canoe=portage tag can still be used as a fallback on ways without a portage tag. Though confusingly, canoe=portage has been used by some mappers on waterways as an indicator that the way is not canoeable (we should probably just fix this in the database).