rename subnavbar stacked

rename subnavbar-stacked to subnavbar_stacked to make it consistent with other configuration options available.
rename subnavbar-stacked to make it consitent.

rename subnavbar-stacked to subnavbar_stacked to make it consistent with other configuration options available.
Merge pull request #625 from pmartelletti/master

Rename subnavbar-stacked to keep consistence