[!!!][TASK] Drop usage of tx_ter_extensionkeys

The database table tx_ter_extensionkeys containing all registered
extensionkeys is dropped in favor of "tx_terfe2_domain_model_extension".

This table was synced already anyways, and can now be used within extensions.typo3.org
without having to sync with a cronjob anymore.

Breaking: The information about "title" and "description" is removed, as it wasn't
required via the Web GUI when registering a key already.

The sync task / TER importer now only imports the uploaded versions, the SOAP API
now creates records directly in tx_terfe2_domain_model_extension when
registering a new extension key.

The One-Time-Migration-Script by tomalo (ImportAllExtensionKeysTask) is
now removed as it is not needed anymore.
6 jobs for feature/drop-extensionkeys in 8 minutes and 13 seconds (queued for 58 seconds)