[modules] Allow modules to provide default click actions

Pass the "output" object to the modules' constructor to allow them to
define their own callbacks.
Any user-provided callbacks take precedence and override those of the
module.

bumblebee/modules/cpu.py

@@ -11,7 +11,7 @@ def description():
     return "Displays CPU utilization across all CPUs."
 
 class Module(bumblebee.module.Module):
-    def __init__(self, args):
+    def __init__(self, output, args):
         super(Module, self).__init__(args)
         self._perc = psutil.cpu_percent(percpu=False)