Resolve "Restructure prior module"

Closes #444 (closed)

bilby/core/prior/base.py

+from importlib import import_module
 import json
+import os
 import re
-from importlib import import_module
 
 import numpy as np
 import scipy.stats
@@ -412,7 +413,7 @@ class Prior(object):
                 module = '.'.join(other_cls.split('.')[:-1])
                 other_cls = other_cls.split('.')[-1]
             else:
-                module = __name__
+                module = __name__.replace('.' + os.path.basename(__file__).replace('.py', ''), '')
             other_cls = getattr(import_module(module), other_cls)
             val = other_cls.from_repr(vals)
         else: