add plugin registry

raven/plugins/filterplugin.py

@@ -0,0 +1,11 @@
+from raven.pluginbase import PluginBase
+
+
+class FilterPlugin(PluginBase):
+    def __init__(self):
+        super(FilterPlugin, self).__init__()
+        print("init FilterPlugin")
+
+
+def init():
+    print("initializing filter plugin")