Doc improvements:

- reorganize title page a bit
- move & update main window description from tutorial to separate page
- move pictures in tutorial in the middle of the text so that the reader
  can follow the pictures
- added short note about number of universes
Merge pull request #147 from janosvitok/docs

Doc improvements

-   reorganize title page a bit
-   move & update main window description from tutorial to separate page
-   move pictures in tutorial in the middle of the text so that the reader can follow the pictures
-    added short note about number of universes
diff to previous version: fixed html, tutorial is separate, moved source img to sources/