Fix #1680 : Add support for custom extension to mime-type mapping
Merge pull request #946 from romainneutron/fix-1680

[3.8] Fix #1680 : Add support for custom extension to mime-type mapping
Merge branch '3.8'
Fix latest merge
Migrate demand table to doctrine entity && refactor registration API
Fix neutron's comment
Fix tests, CS && typo
Rename RegistrationManager to RegistrationManipulator
Adressed Neutron's comments
Refactor && Typo && Use plain objects as function parameters instead of ids
Fix tests & rename RegistrationDemandMigration class