fixed many links and general garbage cleanup of homepage

* fixes nightly link on starting page.
* fixes nightly link on GPGMail page.
* exchange GPGMail FAQ and Getting started link (to the old GitHub
Wiki) and link Tender-KB instead.
* exchanged GPG Keychain Access link to Getting Started (old GH wiki)
to Tender-KB.
* GPGServices added link to workaround (KB-article) for Issue #4.
* Projects page: removed related projects and the single enigmail entry
* Projects page: removed "overview" section (superflouos)