.navbar docs: update -fixed-* callouts, fix -link

* The navbar is now always 50px high, so no need for that nasty padding
code block anymore.
* The new proposed body padding value also reflects the default navbar's
margin-bottom.
* Fixed the navbar-link example positioning (missing .navbar-text).
add detail to navbar component alignment section

* The search form has been deprecated.
* Using pull-* on a list item won't have any effect.
Merge pull request #7882 from juthilo/3.0.0-wip

Cleaning the navbar docs