Implement ChanKeep joining functions

* Low-key channel joining with incrementally increasing delay
* Spin up needed instances to be able to cover a certain channel space
* Fix provisioning functions to prevent race conditions with lots of
relays being created at once
* Tweakable switchover from covering all channels to only covering
channels with more users than the mean of the cumulative user count

modules/network.py

@@ -17,14 +17,16 @@ class Network:
         self.security = security
         self.auth = auth
 
-        self.last = 0
+        self.last = 1
         self.relays = {}
         self.aliases = {}
 
     def add_relay(self, num=None):
         if not num:
-            self.last += 1
             num = self.last
+            self.last += 1
+        elif num == self.last:
+            self.last += 1
         self.relays[num] = {
             "enabled": main.config["ConnectOnCreate"],
             "net": self.net,