Add non-AsciiDoc website landing/home pages

Currently the website is entirely generic from AsciiDoc sources. AsciiDoc generated pages are not very well-suited to serve as home page for a website.

Things to consider:

• We should add custom website home pages.
• It should be attractive, explain what the project or language/tool is about, allow for easy navigation to the rest of the documentation and other websites, etc.
• The rest of the documentation can still be generated from AsciiDoc sources.
• The main download page should contain direct links to download the releases, rather than link to download.eclipse.org.
• The download links should use links that support mirror sites and download statistics. See https://wiki.eclipse.org/IT_Infrastructure_Doc#Use_mirror_sites.2Fsee_which_mirrors_are_mirroring_my_files.3F and https://wiki.eclipse.org/IT_Infrastructure_Doc#See_download_statistics.3F. See also #53 (closed) for enabling download statistics in general.