Added URL checker and corresponding CI job.
- Added a CI job called 'test_urls' that checks all URLs in .py,.rst,.md and .json files and fails in case of dead links.
Note that www.enmap.org is currently white-listed because of a certificate error although the URLs work. I don´t know the reason for this but we have to keep in mind that the CI job will NOT fail in case anything changes in any www.enmap.org related URL in future.
@nbohn You just have to check the output of the CI job, update the remaining dead URLs and then I think you can merge it.
Signed-off-by: Daniel Scheffler danschef@gfz-potsdam.de
Edited by Niklas Bohn