tumblr: pick biggest image based on resolution

[lllusion3469]

photo[:alt_sizes] may contain a bigger image than
photo[:original_size]

fixes #4324

[lllusion3469]

There may be some tests that need to be fixed/added but I would have to set up and environment where I could actually run them first.

Update: tried to get rails test test/unit/sources/tumblr_test.rb test/unit/downloads/tumblr_test.rb to run on my local setup instead of using some complicated docker stuff and it insists on having archive_test set up. Also either rake db:create, rake db:migrate, or rails test deleted my whole public/data directory.