Code review comment for lp:~tpeeters/ubuntu-ui-toolkit/30-optIn-tabsDrawer

I discussed combining pagestack and tabs with Benjamin Keyser, and he agrees that you cannot have flat nav below deep nav (so don't push Tabs on a PageStack), because that would be confusing for the user. This matches the statement "We don’t combine flat with deep navigation in the same view." from http://design.ubuntu.com/apps/global-patterns/navigation