fixes #5041: add new navbar css tests for each variation, remove width: 100%; from .navbar-static-top

Use @bodyBackground on .nav-tabs active state instead of static color

add in some more examples (will work em in later), removed fleetio per their request, and added gather content to replace it

change up box-shadow mixin usage everywhere to use escaping again, or local var if necessary for further var evaluation

fixes #5040 manually: remove overflow: auto; from .modal to resolve sporadic modal right padding issues with scrollbars

Update modal example code to match example