[modules] Add battery indicator plugin

Add a plugin that displays the remaining battery power in %. This also
introduces the concept of arguments that can be passed to a module
during startup by delimiting the module name with ":", for example:

-m battery:BAT1 to query the BAT1 device.

Note that this works to an arbitray length, i.e. if a module accepts 3
parameters: -m <modulename>:<A>:<B>:<C>

The module gets the arguments as list.

i3bumblebee

@@ -28,8 +28,10 @@ def main():
     for m in args.modules:
         # TODO: how to cleanly handle errors here?
         # (useful error messages)
-        module = importlib.import_module("bumblebee.modules.%s" % m)
-        modules.append(getattr(module, "Module")(theme))
+        module_name = m if not ":" in m else m.split(":")[0]
+        module_args = None if not ":" in m else m.split(":")[1:]
+        module = importlib.import_module("bumblebee.modules.%s" % module_name)
+        modules.append(getattr(module, "Module")(theme, module_args))
 
     output = bumblebee.outputs.i3.i3bar()