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
I don't think we should just delete this. There is a changelog on git at https://github.com/dealii/dealii/commits/master . The cdash is still current, as is Timo's page.