add <table> case to responsive-visibility mixin; see 10056

BS3 commits: 303f8a33c354b5c8f6132574de55114b8f39a1f1
fix invalid HTML in components.html. type="button" doesn't make sense for an <a>

BS3 commit: 1d20611d54e813884f3d85a35ccec81add12c6fa
fix .btn-group-xs portion of 10979

BS3 commits: ed0d556847a7a1168a05a6a71f8f1af23139327b
use the @padding-xs-vertical and @padding-xs-horizontal variables. fix the margin and padding for btn-xs in teh navbar.
Add a migration tip for .label to .label-default

BS3 commits: 7b945ad29641444133f3fb8db2b8f3e94332c3f1
add <table> case to responsive-visibility mixin; see 10056. fix .btn-group-xs portion of 10979

BS3 commits: 303f8a33c354b5c8f6132574de55114b8f39a1f1,
ed0d556847a7a1168a05a6a71f8f1af23139327b