Adding mxnet components to rl_coach/architectures (#60)

Adding mxnet components to rl_coach architectures.

- Supports PPO and DQN
- Tested with CartPole_PPO and CarPole_DQN
- Normalizing filters don't work right now (see #49) and are disabled in CartPole_PPO preset
- Checkpointing is disabled for MXNet

rl_coach/architectures/mxnet_components/middlewares/fc_middleware.py

@@ -0,0 +1,52 @@
+"""
+Module that defines the fully-connected middleware class
+"""
+
+from rl_coach.architectures.mxnet_components.layers import Dense
+from rl_coach.architectures.mxnet_components.middlewares.middleware import Middleware
+from rl_coach.architectures.middleware_parameters import FCMiddlewareParameters
+from rl_coach.base_parameters import MiddlewareScheme
+
+
+class FCMiddleware(Middleware):
+    def __init__(self, params: FCMiddlewareParameters):
+        """
+        FCMiddleware or Fully-Connected Middleware can be used in the middle part of the network. It takes the
+        embeddings from the input embedders, after they were aggregated in some method (for example, concatenation)
+        and passes it through a neural network  which can be customizable but shared between the heads of the network.
+
+        :param params: parameters object containing batchnorm, activation_function and dropout properties.
+        """
+        super(FCMiddleware, self).__init__(params)
+
+    @property
+    def schemes(self) -> dict:
+        """
+        Schemes are the pre-defined network architectures of various depths and complexities that can be used for the
+        Middleware. Are used to create Block when FCMiddleware is initialised.
+
+        :return: dictionary of schemes, with key of type MiddlewareScheme enum and value being list of mxnet.gluon.Block.
+        """
+        return {
+            MiddlewareScheme.Empty:
+                [],
+
+            # Use for PPO
+            MiddlewareScheme.Shallow:
+                [
+                    Dense(units=64)
+                ],
+
+            # Use for DQN
+            MiddlewareScheme.Medium:
+                [
+                    Dense(units=512)
+                ],
+
+            MiddlewareScheme.Deep:
+                [
+                    Dense(units=128),
+                    Dense(units=128),
+                    Dense(units=128)
+                ]
+        }