Request data only once
Request data only once

Prevents multiple maps from loading the same data multiple times
This patch also paves way to the future parallel retrieval
of multiple types of external data (geoshapes, web pages)

Bug: T138739
Change-Id: I223f8e528504bee08adbd4bcb0c30f48e01d265f

wikimedia/mediawiki-extensions-Kartographer,wikimedia/mediawiki-extensions-Kartographer,wikimedia/mediawiki-extensions-Kartographer