Remove Theano/Lasagne support

[dniku]

It is hard to maintain support for 3 frameworks (Theano/Lasagne, TF, PyTorch). Since Theano/Lasagne are the oldest ones and have very little traction in the community today, after a discussion with @justheuristic we have decided to remove support for them entirely.

Here is a complete list of files that refer to Theano or Lasagne, obtained via git grep -l -i 'theano\|lasagne'. Legend:

. false positive
~ to be edited
x to be deleted

~ Amazon GPU howto.md
~ Dockerfile
~ docker/Dockerfile
~ week04_[recap]_deep_learning/README.md
~ week04_[recap]_deep_learning/fix_my_nn.ipynb
. week04_[recap]_deep_learning/mnist.py
x week04_[recap]_deep_learning/practice_lasagne.ipynb
. week04_[recap]_deep_learning/seminar_pytorch.ipynb
x week04_approx_rl/homework_lasagne.ipynb
x week04_approx_rl/seminar_lasagne.ipynb
~ week05_explore/README.md
~ week05_explore/bayes.py
~ week05_explore/week5.ipynb
~ week06_policy_based/README.md
x week06_policy_based/reinforce_lasagne.ipynb
~ week06_policy_based/reinforce_tensorflow.ipynb
~ week07_[recap]_rnn/README.md
. week07_[recap]_rnn/arxiv_data.csv
x week07_[recap]_rnn/seminar_lasagne.ipynb
x week07_[recap]_rnn/seminar_lasagne_ingraph.ipynb
~ week07_seq2seq/README.md
x week07_seq2seq/basic_model_theano.py
. week07_seq2seq/basic_model_torch.py
~ week07_seq2seq/bonus.ipynb
. week07_seq2seq/main_dataset.txt
x week07_seq2seq/practice_theano.ipynb
~ week08_pomdp/atari_util.py
~ week08_pomdp/homework_common_part2.ipynb
x week08_pomdp/practice_theano.ipynb
x week08_pomdp/theano_optional_recurrence_tutorial.ipynb
~ week09_policy_II/README.md
x week09_policy_II/seminar_TRPO_theano.ipynb
~ youtube_dl_lectures.sh

week04_[recap]_deep_learning/fix_my_nn.ipynb should have a PyTorch/TF translation elsewhere (DL course?).

Migrating week05 to PyTorch/TF is #174. It is probably going to be easier if that issue is implemented first.