Extract skin hook handlers into ParserOutputHooks

Change-Id: Ie3dea3a69d0a02b91f6dfd0847483c4be4b54b53
Rename ParserOutputHooks to SidebarHookHandlers

The hook handler functions in this class funnel information
from the Parser via ParserOutput and OutputPage into SkinTemplate,
in order to inject links into the sidebar.

Change-Id: I27c7e487d48f11a13a43b256c0790ec4c94c6563
Merge "Extract skin hook handlers into ParserOutputHooks"
Merge "Rename ParserOutputHooks to SidebarHookHandlers"