Change home page layout and remove download button from header

I propose we change the home page layout to single. This will remove the list of subpage links at the bottom of the page which were duplications from the sidebar.

A lot could be done with SEO but I just changed the twitter handle from ECDTools to EclipseFdn.

I also propose we remove the download button. It's confusing that a download button on a documentation page links to a different product. An alternative to this would be to make the button say "Start Chatting" like in the sidebar.