Add option to skip rendering the app's header to prevent re-renders
Move client-side re-hydrating to Y.App subclass

This moves the re-hydrating process to the Y.App subclasses, removing
the work the bootstrapping code has to do. This allows the app to be
dispatched on initialization so it can follow its standard processes for
handling a route, re-hydrating data as needed.
Move template helpers registration into pnm-app module
Merge pull request #14 from ericf/bootstrap

Move client-side re-hydrating to Y.App subclass