subnav for icons section. Fix up navbar forms by using inline form as a mixin; fix docs for those

BS3 commits 7a7971d and 7b6352d
update reference to value of base line-height. More forms overhaul

BS3 commits a19fda6 and 293a3ba
Unitless line-height. More forms overhaul

BS3 commits 6fba68e and 293a3ba