This change is the final change to remove any database tables
from "EXT:ter", and remove any migration from TER v1 (SOAP) to
TER v2 via a scheduler task.

This change removes:
* tx_ter_extensions (versions of an extension)
* tx_ter_extensionqueue (+ its UploadQueue API object)
* ImportExtensionsFromQueueTask (all migrated to ExtensionVersion for now)

All DB rows are written directly into tx_terfe2_domain_model_version and
its related tables.

The API "ExtensionVersion->upload()" now produces everything necessary
including notifications (which can be built via PSR-14 in the future).

This also actually means that extensions are automatically available
RIGHT AWAY after uploading an extension via the GUI or the SOAP API.

Next Steps:
* Refactor our upload API to make it more resistent and moving into a Event Sourcing concept (thinning out all underlying logic from ExtensionVersion again)
* Refactor the permission concept and integrate it nicely
* Remove dependencies to the SOAP API in EXT:ter_fe2