Adds Tropomi download and NOx CSF method

See merge request empa503/remote-sensing/ddeq!3

Update notebook examples and tutorials to work with latest version, fix issues with ERA5 read and download and fix bug with f-model in CSF method working only for one source before

Add and update code for downloading and crop TROPOMI data (change units of distance parameter from km to m)

Make CSF plots look nicer by computing fitted flux 100 times in x-direction instead at polygon center

CoCO2 developments

See merge request empa503/remote-sensing/ddeq!2

Change order of divergence and averaging

Update code, tutorial and example to be more consistent between methods