Changed env var that denotes if we're building for docs.saltstack.com

This one is a bit more descriptive.
Moved Salt version infos to its own sidebar template
Moved quick search to the top of the sidebar
Moved SaltStack events and news to SaltStack-specific sidebar template
Add a little space below the Google Search box
Merge pull request #12390 from whiteinge/doc-sidebar-templates

Shuffle docs sidebars around; move search up to the top