Configure the endpoint exposed through tile.json

The service might sit behind a reverse proxy or other intermediary, so let us for now configure the prefix of the path exposed in tile.json
Merge branch 'master' into filter

Sync with the changes pulled into master
Merge branch 'filter' of https://github.com/LocalData/localdata-tiles into filter

Conflicts:
	tileserver.js
Add config values to the sample environment exporter