[FEATURE] Add ExtensionVersion API
A new API class "ExtensionVersion" deals with a specific uploaded version of an extension. This class is responsible for checking sanitized versions, and serves as entrypoint to hide the logic behind "tx_ter_extensions" (and soon "tx_ter_extensiondetails"), by also handling deletion, updating reviewstate or uploading of new extension versions. On top, all TYPO3_DB calls are removed from EXT:ter with this change, moving more actual logic out of the SOAP API endpoints. In addition, the non-SOAP-API is now using non-static calls, as all logic is wrapped in a doUpload() method.