Add visual indication when working in development/staging environment

If admin menu placed a nice ID or class around the top bar with the site URL, then sites could put:

#dev-example-com .admin_menu { color: "bright, blinding red"; }
#example-com { color: "normal grey"; }
#localhost-example { color: "potato"; }

Into their theme's style.css. Not optimal because it would need to be in both the user-facing theme and the admin theme, but...

Another good reason why we need #464862: Add drupal_css_class() to clean class names and rename form_clean_id in core.

Alternative: Apply this class via JS. (would overcome the edge case of a stale cache after mirroring a site from production to staging/development server).

Not really sure whether I like this entire suggestion, issue, and patch, and whether it's not complete nonsense, but for now, I've committed attached patch to all 3.x branches. Note, however, that I'll revisit this later on.

Thanks for reporting, reviewing, and testing!

A new development snapshot will be available within the next 12 hours. This improvement will be available in the next official release.

oops, here's the patch ;)

Instead of coloring the entire bar (which seems overkill for my tastes), I like the original environment_indicator design option to include a colored button instead: https://vimeo.com/63042899#t=13m32s

However, that doesn't seem to be an option anymore so I've created this patch to simulate the behavior. Note: this is draft quality -- a cleaner solution would move the styling into a CSS file, but I didn't want to modify too many files if no one needed this but me.

Here's the corresponding sample settings.php code:
$conf['admin_menu_environment'] = array('title' => 'local', 'color' => '#0073ba');