[core] Remove alias from module

Hide alias concept for modules in the engine. That way, the individual
modules never get to know about whether a module has been aliased or
not.

see #23

bumblebee/config.py

@@ -35,10 +35,13 @@ class print_usage(argparse.Action):
             print("")
 
 class ModuleConfig(object):
-    def __init__(self, config, prefix):
-        self._prefix = prefix
+    def __init__(self, config, name, alias):
+        self._prefix = alias if alias else name
         self._config = config
 
+    def prefix(self):
+        return self._prefix
+
     def set(self, name, value):
         name = self._prefix + name
         return self._config.set(name, value)