Add a dynamic WFS-based graph updater for adding notes on street edges

As discussed in #1529, I requested for an interface for which dynamic graph updates could be added.

This pull request adds the necessary infrastructure for dynamic street notes services and an implementation of that for WFS-based notes updater. An example implementation of the WFS-based updater can be found at https://github.com/hannesj/OpenTripPlanner/blob/master/src/main/java/org/opentripplanner/updater/WinkkiPollingGraphUpdater.java