KAZOO-304: add token bucket infrastructure to crossbar

Add the crossbar_module_sup back to the mix, for cb_* modules to start their
supervisors under;
cb_buckets_sup is the supervisor for managing the ets table workers and the
kz_token_bucket supervisor;
cb_kz_buckets_sup is the sofo supervisor for the kz_token_bucket servers;
cb_buckets_mgr is the owner and heir of the ETS table, and passes control to the
server used for finding bucket servers
cb_buckets_ets is the interface for reading/creating bucket servers, based on
account_id and client_ip.
KAZOO-304: more strict checking when spawning token bucket server
KAZOO-304: accessor for client_ip from cb_context
KAZOO-304: allow {'halt', Context} as a return from binding server's map
KAZOO-304: start the crossbar_module_sup on startup
KAZOO-304: update skel with formatting, specs
KAZOO-304: add token bucket check to cb_token_auth, before checking token auth
KAZOO-304: fix languages_provided return
KAZOO-304: check for the halt tuple from map and halt processing if found
KAZOO-304: add log to startup of token bucket
KAZOO-304: logging of token counts by account/ip
KAZOO-304: fetch config value with correct key
KAZOO-304: tickies in cb_context.erl
KAZOO-304: move bindings into ets table
KAZOO-304: open doc using open_cache_doc
KAZOO-304: allow req if token bucket server isn't up yet
KAZOO-304: stop the token bucket supervisor
KAZOO-304: add logging to v1_resource
KAZOO-304: parse_path_tokens doesn't check the filesystem

We try to call cb_module:module_info() to see if the cb_* module exists
rather than checking the filesystem for the beam file
KAZOO-304: tickies for couch_mgr