various improvements

[EvanBldy]

Problem

• Black
• All JTI are registered in redis we need only to use redis as a blocklist.
• Some requirements are outdated.
• Some plugins for OTIO are missing due to upgrading to last version (see here: https://github.com/AcademySoftwareFoundation/OpenTimelineIO/releases/tag/v0.17.0)
• Some files (project thumbnails for example) are not properly redownloaded due to the cache (max age HTTP header). We need to add a last_modified header.

Solution

• Black
• Upgrade outdated requirements.
• Only use redis as a blocklist for JTIs.
• Add OpenTimelineIO-Plugins to requirements for any plugins like EDL, XML, etc.
• Add a last_modified header for every file + refactoring.