merge 3.19.4 in 3.20 branch

[cors] Fix CORS headers generators The Access-Control-Allow-* and Access-Control-Expose-Headers are response headers, not request headers. Hence, we need generators for them. Closes #4412575.

[wsgi] Fix posted files filename reading The filenames are parsed by multipart.parse_form_data, which does the unicode decoding. Trying to re-decode the filename was leading to an error.

[pkg] Depend on Pillow instead of PIL The Pillow library is becoming the de-facto replacement for PIL. It also is way simpler to install with pip than PIL. Closes #4411354.

Added tag cubicweb-version-3.19.4, cubicweb-debian-version-3.19.4-1, cubicweb-centos-version-3.19.4-1 for changeset c4e740e50fc7

[pkg] 3.19.4

merge 3.18.6 into 3.19

Added tag cubicweb-version-3.18.6, cubicweb-debian-version-3.18.6-1, cubicweb-centos-version-3.18.6-1 for changeset d91501356742

[pkg] 3.18.6

[hooks/security] allow edition of attributes with permissive permissions If an attribute has more permissive security rules than the entity type itself, we should be green and not deny action because of an early global entity permission check (with the more restrictive rules). Only if one attribute with the entity-level permission rules is edited will the global check be performed. Note: * the "if action == 'delete'" check at the entry of check_entity_attributes is a guard for a condition currently not happening in cubicweb itself (but application hooks could conceivably call this function with a 'delete' action) Closes #3489895.