Cleanup imports.

Till now, most of the modules were importing all of the module objects
(variables, classes, functions, other imports) into module namespace,
which potentially could (and was) cause of unintentional use of class or
methods, which was indirect imported.

With this patch, all the star imports were substituted with top-level
module, which provides desired class or function.

Besides, all imports where sorted (where possible) in a way pep8[1]
suggests - first are imports from standard library, than goes third
party imports (like numpy, tensorflow etc) and finally coach modules.
All of those sections are separated by one empty line.

[1] https://www.python.org/dev/peps/pep-0008/#imports

exploration_policies/__init__.py

@@ -1,5 +1,5 @@
 #
-# Copyright (c) 2017 Intel Corporation 
+# 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.
@@ -13,16 +13,29 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
+from exploration_policies.additive_noise import AdditiveNoise
+from exploration_policies.approximated_thompson_sampling_using_dropout import ApproximatedThompsonSamplingUsingDropout
+from exploration_policies.bayesian import Bayesian
+from exploration_policies.boltzmann import Boltzmann
+from exploration_policies.bootstrapped import Bootstrapped
+from exploration_policies.categorical import Categorical
+from exploration_policies.continuous_entropy import ContinuousEntropy
+from exploration_policies.e_greedy import EGreedy
+from exploration_policies.exploration_policy import ExplorationPolicy
+from exploration_policies.greedy import Greedy
+from exploration_policies.ou_process import OUProcess
+from exploration_policies.thompson_sampling import ThompsonSampling
 
-from exploration_policies.additive_noise import *
-from exploration_policies.approximated_thompson_sampling_using_dropout import *
-from exploration_policies.bayesian import *
-from exploration_policies.boltzmann import *
-from exploration_policies.bootstrapped import *
-from exploration_policies.categorical import *
-from exploration_policies.continuous_entropy import *
-from exploration_policies.e_greedy import *
-from exploration_policies.exploration_policy import *
-from exploration_policies.greedy import *
-from exploration_policies.ou_process import *
-from exploration_policies.thompson_sampling import *
+
+__all__ = [AdditiveNoise,
+           ApproximatedThompsonSamplingUsingDropout,
+           Bayesian,
+           Boltzmann,
+           Bootstrapped,
+           Categorical,
+           ContinuousEntropy,
+           EGreedy,
+           ExplorationPolicy,
+           Greedy,
+           OUProcess,
+           ThompsonSampling]