Removed tensorflow specific code in presets (#59)

* Add generic layer specification for using in presets

* Modify presets to use the generic scheme

rl_coach/architectures/tensorflow_components/utils.py

@@ -0,0 +1,40 @@
+#
+# Copyright (c) 2017 Intel Corporation
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+"""
+Module containing utility functions
+"""
+import tensorflow as tf
+
+
+def get_activation_function(activation_function_string: str):
+    """
+    Map the activation function from a string to the tensorflow framework equivalent
+    :param activation_function_string: the type of the activation function
+    :return: the tensorflow activation function
+    """
+    activation_functions = {
+        'relu': tf.nn.relu,
+        'tanh': tf.nn.tanh,
+        'sigmoid': tf.nn.sigmoid,
+        'elu': tf.nn.elu,
+        'selu': tf.nn.selu,
+        'leaky_relu': tf.nn.leaky_relu,
+        'none': None
+    }
+    assert activation_function_string in activation_functions.keys(), \
+        "Activation function must be one of the following {}. instead it was: {}" \
+            .format(activation_functions.keys(), activation_function_string)
+    return activation_functions[activation_function_string]