Land cover and other grids for whole countries, in seconds

Changes since 2.14.0.

#Fixed

• Land cover for a whole country. Asking for land cover per area across a whole country (for example "built-up area in each county of Kenya" or "tree cover share by region in Uganda") used to run past the time limit, because Orion read the 10 m land cover map at full detail even when the result was drawn at a few hundred metres. Orion now reads it at the detail the map needs: reading the land cover for all of Uganda takes about 5 seconds instead of more than 11 minutes. The same change speeds up elevation and other tiled grids over large areas.
• One slow step no longer fails others. When an analysis step ran past its time limit, other steps running at the same moment (including other people's) could fail with "This step needed more memory than allowed". Each step now runs on its own, so only the slow step stops.
• Rainfall problems are reported plainly. When the CHIRPS rainfall server refuses Orion's requests, OrionAI now says that rainfall is unavailable for now, instead of "rainfall has no data in this area" and trying one period after another.

#Improved

• Rainfall is kept on Orion. Each month of CHIRPS rainfall is downloaded once and then read from Orion's own copy, so repeat requests are faster and put far less load on the Climate Hazards Center's server.