Change links on docs sidebar

* Remved "Older Versions" section that contained broken links
* Fixed link to pytest
* Fixed "Current Version" link to pypi to link to current version
* Removed link to old and unused announcement mailing list

This fixes #374
Merge pull request #679 from Infinidat/374

Fix #374: "Older Versions" link broken on home page, and a few other issues.