Register S1 image downloading as Dask tasks
Currently (v0.2), S1Processor.py
loops on all S2 tiles requested. For each S2 tiles, after a dependency analysis (#22 (closed)), all intersecting S1 images are downloaded, then the processing is started.
Instead, it could be interesting to register the downloading of S1 images as dask tasks that calibration+cutting depends upon. This would give more flexibility for S2 tiles for which of subset of intersecting S1 images are already downloaded: this would reduce the overall latency during the execution: we could download and process at the same time, and so on.