adapt the routing helper, so it also works for bicycle route relations

[Polyglot]

During the summer of 2018, the routing helper was added to help the user add ways in a more convenient way than selecting, adding, resorting route relation, splitting ways, etc.

It would be really helpful to add this functionality for bicycle and foot route relations. In bicycle route relations the extra complication is that both directions are described with a single route relation, so it might be a bit harder to accomplish. When the route forks due to oneway traffic, it's probably needed to work on one 'leg' at a time.

It will also be good to reorder the remaining ways at every step, to see whether they 'fall in place'. It may be necessary to propose to change roles from forward to backward and vice versa and maybe even to remove such roles.

It seems to me that it would be necessary to keep track of whether one is on a common part of the route, or in the section of a fork going from A -> B, or working on a section going from B -> A.
While going from A->B always check if the end of the fork was reached and it's needed to switch to BA mode. While in BA mode, again check if the end of the fork is reached (by now it's clear where that occurs) and switch to common ways mode again.