Issues/1.0.7 (mainly #636)

[Fasand]

• site.webmanifest static URL fix
• new utility command generate_unique_seeds --base-url --num --output to generate unique seeds for testing large custom seeds upload
• add Topic Collection custom_seeds backup functionality into media/seeds/backup
• source XLSX export is now login-protected
• limit počtu semínek #636 enable upload of very large custom_seeds through a TXT file
  • TC edit form doesn't allow manual edit of custom seeds when there's more than 1MB of them, only overwriting
  • seeds only get paired when there's a small number of seeds (<1MB)
  • TC saves are optimized to not save custom_seeds if not necessary (becomes a big problem when size is in 10s of MB)