AA-167: Making icon_class dynamic for LTI

[BD-6] Compliance with OEP-18

Remove constraints.
Add classifiers.
Update setup.py install_requirements definition.
Update travis file using new requirements.
Create requirements folder.
create pip_tools, base, test and travis requirements files.
Remove old requirement files.
Create Makefile and add upgrade command.
Include requirements files generated using upgrade command.
Update openedx.yml OEPs list.

Show graded unit icon

This shows the 'problem' icon for LTI units, rather than the default
'other' icon.

AA-75

Updated fragment import to remove depreciation warning

removed web_fragment deprication warnig

fixed import sequece

Added img to bleach safe tags

updated bleach

Added img to bleach safe tags

Added img to bleach safe tags

Added img to bleach safe tags

added test

added test

added test

added test

added test for attr image

added test for attr image

fixed style bug

Updated format xoe

removed extra formatting

avoid-escape-exception

Handle case when we don't have to turn body into a bytestring.

Handle case where body may or may not be unicode.

Upgrade to pyhton 3.

Updated to run tests on both python 2 and 3.

PROD-774

Update translations (autogenerated message)

Update translations (autogenerated message)

Add metadata for oep-2 compliance.

Allow plugins for the LTI XBlock to pass extra parameters to the provider

Overview
---------
This pull request makes this XBlock extensible for
adding parameters to the LTI provider in addition
to the existing ones.

Why
---
A customer needs `team` and `cohort` informaiton
to be passed through the LTI channel to simplify
integration with their LTI provider. At the same
time we'd rather not fork the XBlock, so an
Open-Closed model is needed.

More Detailed Documentation
---------------------------
I've added a couple of sections to `README.rst`
to document specifying design and
configuration steps of the new LTI parameter
processors. Please check it out for more
information about the changes that this pull
request introduces.

Example Usage
-------------
I've written a package that we'll need to use for
our customer to pass some personal user
information in addition to the cohort and team
info: https://github.com/appsembler/tahoe-lti/pull/1

Omar Al-Ithawi @ Appsembler

Add context_title and context_label parameters

Add context_label and context_title to LTI POST parameters; Add required requirements; add some docker devstack instructions;

Additional allowances given to iframe due to the following chrome update from version 64:
https://dev.chromium.org/Home/chromium-security/deprecating-permissions-in-cross-origin-iframes

noraiz/EDUCATOR-1218-fix