allow class methods to be passed to hyper model

This will allow users to pass class methods to the hyper model by enforcing that certain argument names can't be used.

bilby/hyper/model.py

@@ -30,6 +30,11 @@ class Model(object):
         return probability
 
     def _get_function_parameters(self, func):
+        """If the function is a class method we need to remove more arguments"""
         param_keys = infer_parameters_from_function(func)
+        ignore = ['dataset', 'self', 'cls']
+        for key in ignore:
+            if key in param_keys:
+                del param_keys[param_keys.index(key)]
         parameters = {key: self.parameters[key] for key in param_keys}
         return parameters