Issue #254 Replace logo by one with smaller title font.
Issue #254 Emphasize that the former advisors are no longer actively involved.
Issue #254 Remove people and references to SBIA from help page.
Issue #254 Provide clearer download links.
Issue #254 Cleanup header of .rst files.

The Subversion keywords have no more meaning after moving to Git. These headers were anyway requested for by the system administrator at SBIA and are thus now obsolete after the project moved to GitHub.
Issue #254 Rename .rst files for consistent URLs and naming scheme.
Issue #254 Remove remaining obsolete dependencies tag.
Issue #254 Clean up API Reference index page.
Issue #254 Change title of installation page.
Issue #254 Change title of quick start section.
Issue #254 Move full table of contents to separate page.