For everything before 2015 an OAR copyright is assumed. Later copyright
notices are based on Git commits on a best effort basis.
The copyright notices of the "RTEMS Software Engineering Handbook" and
the "RTEMS CPU Architecture Supplement" are incomplete.
- Remove all genindex.rst files, these are generated and should not
exist in our source.
- Fix the HTML templates so the local specialisation works.
- Add a index link to the sidebar for HTML.
Note, there is no TOC entry for the index in the PDF output and I
cannot figure out how to add one.
Closes#3503
