Push replication

[jpoyau]

Add code it implement pull/push replication. It implements a service that allows a node to push it data through couchdb replication to any couchdb database. To pull data from any node that implements this service one needs to do a post to<node_url>/push_to the following data:

{
   "destination_database_url": "<url>",  //couchdb target database url required
   "include_exclude"': true/false,
   "filter": // array of filter rules optional
         [
              {"filter_key":"string", // REGEX that matches names in the
                                            // resource data description
                                            // required
              "filter_value": "string" // REGEX that matches values in the
                                            // resource data description
                                            // optional, if not present, any value matches
                }
         ],
   "predicate": "function(doc){... return true;}" // javascript predicate function that takes a 
                                                                // doc and return true or false optional
}