Rework some ReST stuff to remove warnings.

 deleted:    Documentation/Chapter1/Index.rst
 modified:   Documentation/Extbase/Index.rst
 renamed:    Documentation/Targets.rst -> Documentation/FinalPages/Targets.rst
 modified:   Documentation/FirstExtbaseExtension.rst
 modified:   Documentation/Index.rst
 modified:   Documentation/Introduction/Index.rst
 deleted:    Documentation/NextSteps/Index.rst
 modified:   Documentation/Settings.yml
 new file:   Documentation/Sitemap/Index.rst
 modified:   Documentation/Step1Introduction/DependencyInjection.rst
 modified:   Documentation/Step1Introduction/DomainDrivenDesign.rst
 modified:   Documentation/Step1Introduction/Index.rst
 modified:   Documentation/Step1Introduction/Introduction.rst
 modified:   Documentation/Step2SystemCheck/Index.rst
 modified:   Documentation/Step2SystemCheck/Php.rst
 modified:   Documentation/Step2SystemCheck/Typo3.rst