Add flags --site-middleware and --om-tools, split off a cljs dev namespace

Give people the choice between running an API style site at the
backend (the default, use compojure.handler.api middleware), or build an
HTML rendering site (--site-middleware, uses compojure.handler.site).

Give people the choice to use om-tools.dom instead of
om.dom (--om-tools)

Put the development specific stuff in separate dev namespaces to reduce
the clutter.