[BD-2] BB-2365: Merge LTI 1.3 support to master. 

k# Please enter the commit message for your changes. Lines starting

Also fixes a few untreated exceptions and remove unused variables.

Signed-off-by: Giovanni Cimolin da Silva <giovannicimolin@gmail.com>

Signed-off-by: Giovanni Cimolin da Silva <giovannicimolin@gmail.com>

This commit adds support for the LTI 1.3 Access token endpoint, as detailed in the IMS Security Framework.
The token is generated using the consumer's private key (stored in the XBlock) after validating the message sent by the LTI Tool using it's public key.

Signed-off-by: Giovanni Cimolin da Silva <giovannicimolin@gmail.com>

Features:
Implement LTI 1.3 launch support.
Add LTI 1.3 passthrough views as LMS plugins.

Features:
Implement LTI 1.3 launch support.
Add LTI 1.3 passthrough views as LMS plugins.

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.