Added logo to mainpage

git-svn-id: http://www.openflipper.org/svnrepo/OpenFlipper/branches/Free@5481 383ad7c9-94d9-4d36-a494-682f7c89f535

Doxygen/mainpage.docu

 /*! \mainpage Mainpage
- *
+ *\image html splash.png
  * \section intro_sec Introduction
  *
  * This is the developer documentation for the OpenFlipper project.