Data retraceable to datapoint in geojson on github

[ElmarJ]

This feature creates a link from any object in the simulation back to the original geojson feature on github. For this to work, we need two things:

• Unique identifiers for all geojson features, stored in the game-objects that represent these features. Depends on Add unique identifiers to all objects waterlooplein-timemachine-gisdata#8
• A property on the game object containing the link to the original file on Github

This enable several interesting features:

• Update auto generated content directly from the Github source, without having to manually copy the files
• Generation of content at runtime, directly from geojson source online
• Update feature data straight from within the simulation environment, generating a pull request to the original data file

Solve together with #9

[ElmarJ]

Unique identifiers are there, but second step is much easier to solve after ElmarJ/GeoJsonCityBuilder#6 has been dealt with, so will have to wait a bit longer.