Rename .hero-unit to .jumbotron becaue fuck dashes in filenames and sports metaphors are cooler than ad ones

this is a resubmission of #5875, but now against branch 3.0.0-wip
does not exclude elements under a fieldset's legend
issue #6058 is a duplicate of #5605

* Deprecate .input-append and .input-prepend
* Use new, single base class for component, .input-group
* Deprecate .addon for .input-group-addon
* For compatibility with all buttons, require .input-group-btn to wrap buttons and button dropdowns
* Still need to reimplement with segmented button dropdowns, but that's dependent on a refactor of those first

* Scopes striping to immediate children of the tbody and tr
* For nested tables, sets a background color of @bodyBackground, to override the default transparent bg

* Add simple test to css-tests.html
* Scope .table-bordered to immediate children th/td elements only