"updated old-legacy TF version for a better compatibility"

[ofpol]

• added old legacy compatibility, updated gitignore
• updated Tensorflow Version
  After running the deep_q_network.py file, I've encountered an old-legacy TF version incompatiblity.
  Which requires me to downgrade TensorFlow version from 2.X up to 0.7, doing so would break linux
  system dependencies. Instead I have changed the hard coded following line:

import tensorflow as tf

to

import tensorflow.compat.v1 as tf
tf.disable_v2_behaviour()

for making the code more portable, and giving people freedom to use their newer tf => 1.15.0 versions.