Missing-observation-autocomplete (#231)

* add types

* return type

rlbench/demo.py

@@ -1,17 +1,19 @@
 import numpy as np
+from typing import List
+from rlbench.backend.observation import Observation
 
 
 class Demo(object):
 
-    def __init__(self, observations, random_seed=None, num_reset_attempts = None):
+    def __init__(self, observations: List[Observation], random_seed=None, num_reset_attempts=None):
         self._observations = observations
         self.random_seed = random_seed
         self.num_reset_attempts = num_reset_attempts
 
     def __len__(self):
         return len(self._observations)
 
-    def __getitem__(self, i):
+    def __getitem__(self, i) -> Observation:
         return self._observations[i]
 
     def restore_state(self):