Supporting vector tiles

[SimonbJohnson]

ITOS will start publishing vector tiles for some country admin boundaries. This approach could allow implementation of lower level admin boundaries, but reducing tile transfer.

An example of the test service here:
https://simonbjohnson.github.io/HDX_tile_map_test/index2.html

Their server does not have compression, so need to assess file size and compare to approach consider here of separating large country files in multiple files.

#64