Adding form class with modified suffixes needs manual adjustment of pro file

Steps to reproduce:

• create a Qt Widgets Application
• create a new Qt Designer Form Class for this project
  • on the Class Details page give the header and the source file a not-so-common suffix (I've used .H for the header, .CC for the source)
• check the navigator and/or the pro file

Current result:

• although the wizard had information about the file name for the source file it seems as if Creator tried to figure out the mime type for this file and placed it to the headers instead of the sources
• this is even more weird as the icon for the file is an icon for a source file