Conflation project

[Gigaszi]

This adds support for the Conflation project type to MapSwipe web. Conflation allows users to validate building footprints from fAIr or other sources, and compare them against potentially existing OpenStreetMap features.

Tasks of conflation projects consist in building footprint geometries. The web app requests all current OSM buildings within the bounding box of all task features in a task group. The nature of each task changes depending on the presence of buildings in OSM:

• If there are no OSM buildings that intersect with the current task feature, the task behaves like a standard validate project task.
• If there is exactly one OSM building intersecting with the task feature, the user is asked to evaluate which of the two ones is correct.
• If there are two or more OSM buildings intersecting with the task feature, the task is skipped.

Together with the results, the web app writes the number of intersecting OSM features to Firebase, and, if that number is 1, the OSM id and version number of that building.

MapSwipe does not commit any changes to OSM at this stage of the implementation.