fixes #4044: make z-index of tooltips same as fixed navbar so they overlay it if generated from within

fixes #4444: clarify docs copy that new icon white style is intentional on active and hover links in .nav and .dropdown-menu

fixes #4445: .btn-link shouldn't have a pressed button-like state at all, so nuking everything on :active as well

fixes #4260 and #4322: set vertical-align to top on input-prepend components to solve modal rounding issues