Add LINZ (Land information new zealand) imagery layers about editor-layer-index HOT 3 CLOSED

Concerning of aerial images: The layer to go is https://creativecommons.org/licenses/by/3.0/nz/ since it combines all individual aerial layers. Many aerial layers are licensed CC BY 3.0 NZ which is not compatible with OSM unless a special agreement can be made. When the license question is clarified, an API key is required as explained on https://data.linz.govt.nz/set/2-nz-aerial-imagery/webservices/

from editor-layer-index.

I'm in talks with LINZ about the licensing question. LINZ did provide an explicit permission previously, but I'm seeking to clarify this covers imagery as well, and make this more legally solid by using the waivers from the OSMF https://blog.openstreetmap.org/2017/03/17/use-of-cc-by-data/.

from editor-layer-index.

I've received a positive response from LINZ. They have completed the OSMF waiver (slightly tweaked for the NZ CC BY license)

https://wiki.openstreetmap.org/wiki/File:OSM_waiver_-_LINZ.pdf

PR at #334

from editor-layer-index.