add controls to match grids

[mdsumner]

• record zoom on object (https://twitter.com/mdsumner/status/1269204969325948931?s=20)
• allow direct matching of grids (when input grid is Mercator, with clear derivation was from tiles), or by option
• consider removing 2x thing for elevation, so it matches by default!
• consider output that is a combo image+elevation (4 layer raster?)