add a catch_all plugin function to see all messages from slack

rtmbot.py

@@ -80,6 +80,11 @@ class Plugin(object):
                 eval("self.module."+function_name)(data)
             except:
                 dbg("problem in module")
+        if "catch_all" in dir(self.module):
+            try:
+                self.module.catch_all(data)
+            except:
+                dbg("problem in catch all")
     def do_jobs(self):
         for job in self.jobs:
             job.check()