Let DS keep free Kiwi slots enhancement

[doccodyblue]

As an enhancement I would vote for the following:

• Define a minimum of free slots per RX in the config
• Before starting a new worker, check KiwiSDRs /status and pull "users" and "max_users"
• If max_users - users < minimum_free_slots, put DS to sleep for a while

This way, we could let DigiSkimmer run on an idle receiver but keep a slot free if the RX is getting really busy during "rush hour"

I am not advanced enough to find the right spots to implement and do a PR. As an example I did it like that in the run method of KiwiWorker:

`# check if enough slots free for digiskr
parsed_list = {}
min_free_ports = 2
url = "http://"+str(self._options.server_host)+":"+str(self._options.server_port)+"/status"
print("Asking " + url + " for free ports")
response = urlopen(url)
string = response.read().decode('utf-8')
list_string = string.split('\n')

        for item in list_string:
            if item:
                key, value = item.split("=")
                parsed_list[key] = value

        if int(parsed_list['users_max']) < int(parsed_list['users']) + min_free_ports:
            print("not enough free slots")
            self.connect_count -= 1
            if self._options.connect_timeout > 0:
                self._event.wait(timeout = self._options.connect_timeout)

`

Please excuse for the beginner style python. I didn't find the right spot to check users on every freq change, but maybe you get the idea and I am sure this could be useful for others as well.