Encrypt the session id before writing to tracking logs.
Also use md5 for constructing key for hmac.
Fixes BLD-1104
Add additional tests for tracking of sessions.
Merge pull request #3962 from edx/dcs/BLD-1104

Fixes BLD-1104
Product stack documentation

DOC-448
fix nfsd in devstack
Move .pep8 content to setup.cfg
locking version of requests-oauthlib to 0.4.0

requests version 1.2.3 does not appear to be compatible with the
new version of requests-oauthlib.

requests-oathlib tries to import to_native_string in util.py:

```
File
"/root/.virtualenvs/edx-platform/local/lib/python2.7/site-packages/requests_oauthlib/oauth1_auth.py",
line 10, in <module>
    from requests.utils import to_native_string
ImportError: cannot import name to_native_string
```
Added logging for sender email address on BotoServerError.
LMS-2734
Merge pull request #3978 from edx/waheed/lms2734-added-logging-for-email

Added logging for sender email address on BotoServerError.
Update database caches to include latest migrations
Merge pull request #4024 from edx/will/test-speedups

Update test database cache
Serve ORA2 JavaScript i18n strings
Merge pull request #4001 from edx/will/ora2-i18n-js-strings

Serve ORA2 JavaScript i18n strings
Merge pull request #4023 from edx/jarv/downgrade-requests-oauthlib

locking version of requests-oauthlib to 0.4.0
Merge pull request #3954 from edx/brian/fix_session_id

Encrypt the session id before writing to tracking logs.
making system status notifications flexible based on content
Merge pull request #4002 from edx/db/move-pep8-to-setup-cfg

Move .pep8 content to setup.cfg
Fix performance regression
Remove course_from_id
don't fetch whole course when the root will do
don't fetch even the root if the id will do
check for definition.data == null