[TYPO3-mvc] sr_feuser_register, set tx_extbase_type

[Tim Schoch | GSTALTIG]

You are a genius!

The missing piece was this little snippet: 
-- constants ---------
  plugin.tx_sremailsubscribe.formFields := addToList( 
  module_sys_dmail_html,module_sys_dmail_cateogry,tx_extbase_type)
  ------------------------

The edit Fields where not necessary, only the above. But now I'll have to figure out, how to hide the HTML Mail checkbox 
in the user form... But I'll tackle this by my own, thank you for your help guys.

Tim