Restructure index template page.

The high-level entry into the documentation is now in the index.
Add link to Doxygen documentation, remove api link.
Remove api link.
Initial dummy version
Remove
Adapt filenames so that the menu points to existing documents.
Moved to modules directory.
Derive from GBase.
Split document in chapters and revise text.
Remove original document
Correct Doxygen documentation link
Set version number to 0.8.0pre