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

logger.py

@@ -13,19 +13,16 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 #
-
-from pandas import *
+import datetime
 import os
 import re
-from pprint import pprint
-import threading
-from subprocess import Popen, PIPE
-import time
-import datetime
-from six.moves import input
-from PIL import Image
-from typing import Union
 import shutil
+import time
+import typing
+
+import pandas
+import PIL
+from six.moves import input
 
 global failed_imports
 failed_imports = []
@@ -90,7 +87,7 @@ class ScreenLogger(object):
     def ask_input(self, title):
         return input("{}{}{}".format(Colors.BG_CYAN, title, Colors.END))
 
-    def ask_yes_no(self, title: str, default: Union[None, bool]=None):
+    def ask_yes_no(self, title: str, default: typing.Union[None, bool]=None):
         """
         Ask the user for a yes / no question and return True if the answer is yes and False otherwise.
         The function will keep asking the user for an answer until he answers one of the possible responses.
@@ -156,7 +153,7 @@ class BaseLogger(object):
 class Logger(BaseLogger):
     def __init__(self):
         BaseLogger.__init__(self)
-        self.data = DataFrame()
+        self.data = pandas.DataFrame()
         self.csv_path = ''
         self.doc_path = ''
         self.aggregated_data_across_threads = None
@@ -249,7 +246,7 @@ class Logger(BaseLogger):
         if not os.path.exists(output_dir):
             os.makedirs(output_dir)
         output_path = os.path.join(output_dir, output_file)
-        pil_images = [Image.fromarray(image) for image in images]
+        pil_images = [PIL.Image.fromarray(image) for image in images]
         pil_images[0].save(output_path, save_all=True, append_images=pil_images[1:], duration=1.0 / fps, loop=0)
 
     def remove_experiment_dir(self):