Add Global Wind Atlas as contextual layer

[vgeorge]

Browser the map here.

This is an example tile query:

• https://s3-eu-west-1.amazonaws.com/globalwindatlas2/pd_250_ad_100m_linear/9/278/286.png

It seems that the source tileset does not use Web Mercator Projection or is a TMS service. We need to investigate and add it as a layer with MapboxGL.

See:

• https://github.com/global-electrification-platform/explorer/issues/218
• https://gist.github.com/tmcw/4954720#file-xyz_vs_tms-md

[nicolinalindblad]

@bpstewar you mentioned that it won't be possible to add the atlas at this time?