Offline-documentation cleanup

This patchset cleans up the offline documentation:

 * Update old references to svn with references to git

 * Remove direct links to online resources - Those do not belong into the
   offline documentation, and are already easily available on the homepage.

 * Remove stub content that only pointed to online location

 * Unify indentation stuff
Already integrated in doc/doxygen/headers/coding_conventions.h directly at the top.