implement k-choices join functions

large commit, contains a number of things:
- k-choices #2 cost calculation
- k-choices parameters
- adjusting ASN.1 network messages to contain all values required for
  cost calculation #71
- adjusting stats to contain required values
- k-choices node and vserver join functions
- placeholder/ dummy invocation of k-choices join

app/Main.hs

@@ -49,6 +49,9 @@ readConfig = do
           , confRequestTimeout = 5 * 10^6 `div` speedup
           , confRequestRetries = 3
           , confEnableKChoices = loadBalancingEnabled /= "off"
+          , confKChoicesOverload = 0.9
+          , confKChoicesUnderload = 0.1
+          , confKChoicesMaxVS = 8
           }
         sConf = ServiceConf
           { confSubscriptionExpiryTime = 24*3600 / fromIntegral speedup