Use multiple dispatch lists instead of multiple routers.

Since the ets table holding the dispatch lsit is public, there's no
reason to start multiple router processes. Instead, we just change the
key of the stored dispatch list to be the name, defaulting to
`webmachine_router`.
Distinguish the listener name from the router/routes name.
Only convert the name if it's not already a list.
If the name is not given, use 'webmachine'.
Rename router_name -> dispatch_group and webmachine_router -> default.
Merge pull request #128 from basho/sdc-fix-multiple-routers

Bugfix for multiple routers under Riak