Upgrade to python3

[johnbradley]

Changes:

• Upgrades to python3
• Updates requirements to fix https://nvd.nist.gov/vuln/detail/CVE-2017-16876 and update python3 incompatible requirements

NOTE:
The deployed Docker image contains both python3 and python2. Ideally this would just contain python3. This repo runs some CWL workflows that are based on external repositories that are not upgraded to python3:

iMADS-worker/Dockerfile

Lines 36 to 45 in fffd8a4

	### Step 3: Install Predict-TF-Binding from GitHub
	WORKDIR /opt/
	RUN git clone https://github.com/Duke-GCB/Predict-TF-Binding.git predict-tf-binding
	RUN pip install -r /opt/predict-tf-binding/requirements.txt
	ENV PATH /opt/predict-tf-binding/:$PATH
	### Step 4: Install Predict-TF-Preference from GitHub
	WORKDIR /opt/
	RUN git clone https://github.com/Duke-GCB/Predict-TF-Preference.git predict-tf-preference
	ENV PATH /opt/predict-tf-preference/:$PATH

Fixes #15
Fixes #17

This is currently deployed/tested on http://imads-dev.gcb.duke.edu.

[dleehr]

LGTM. Created Duke-GCB/Predict-TF-Binding#45 and Duke-GCB/Predict-TF-Preference#4 to upgrade those projects to Python 3