Refactor launcher to be object-oriented (#63)

* Import of annoy library uses failed_import mechanism.

rl_coach/memories/non_episodic/differentiable_neural_dictionary.py

@@ -18,7 +18,12 @@ import os
 import pickle
 
 import numpy as np
-from annoy import AnnoyIndex
+try:
+    import annoy
+    from annoy import AnnoyIndex
+except ImportError:
+    from rl_coach.logger import failed_imports
+    failed_imports.append("annoy")
 
 
 class AnnoyDictionary(object):
@@ -283,4 +288,4 @@ def load_dnd(model_dir):
 
             DND.dicts[a].index.build(50)
 
-    return DND
+    return DND