adds support for line-height property, fixes a blocking bug in length units menulists, fixes a bug in Border Tab when trying to unspecify the border style and all four side borders have the same styles
CaScadeS landing, doc only change, b=161663, r=brade, a=rjesup@wgate.com
CaScadeS landing, b=161663, r=brade, a=rjesup@wgate.com