Add header categories and site navigation to small sidebar

• Add new icons: refreshed-collapsible-expand,

refreshed-collapsible-collapse

• Add header category collapsible sections to the sidebar on

small

• Add site navigation collapsible section to the sidebar on

small

• (Potential goal for next commit: switch to LESS, cut down on

unused classes/IDs)

Change-Id: I3df001b56e2fb4fa84e02c4ff6a702cbe1f4de23