Use local reference to Network in constructor

To allow customizing the bc module in compatibility wrappers, use the
local reference instead of a global one.  This means a wrapper module
could set `BaseControl.Network` to a different default.

bc.lua

@@ -139,7 +139,7 @@ function BaseControl:new(network)
     listeners = {},
 
     live = false,
-    network = network or Network:new(),
+    network = network or BaseControl.Network:new(),
   }
   setmetatable(self, {__index=BaseControl, __call=BaseControl.new})