Make download_all() method auto increment over pages to download all found pages at once.

• Add a parameter to download_all() to enable pages auto-iteration or not
• On search, save search params in SearchResults object the same way it is done at EOProduct level
• On crunch, save crunch params in SearchResults object, and apply it on next pages
• we may add a generator to SearchResults for auto-iteration, like a .next_page() method

When using download_all on a paginated SearchResult, page iterator should be automatically used to fetch next pages products:

prods, found_nb = dag.search(**query_args) # len(prods)=20, found_nb=300

paths = dag.download_all(prods, exhaust=True) # len(paths)=300
paths = dag.download_all(prods) # exhaust=False by defaut,  len(paths)=20