Adding resource_link_id template tag for adding the resource link id to form submission GET requests

Add additional middleware to support multiple LTI launches and retain backwards compatibility of the current single launch middleware

Don't store LTI_OAUTH_SETTINGS during module load so that functional tests can override settings on each tests run - the auth_lti backend is imported once as an AUTHENTICATION_BACKEND during project load so storing the settings at the top of the module prevents overriding of this setting during authentication.  Up version to 1.0 (current Github release is at 0.9, so this is another minor bump).

adds error check for when settings.LTI_OAUTH_CREDENTIALS is None or {}, which is possible due to improperly configured ENV_SETTINGS in a project

Modify logic for picking a default username value when lis_person_sourcedid parameter is not present.  It's believed that this should only be the case when user is added directly in Canvas UI and when admins switch to "Student View" mode.  Use custom_canvas_user_id (or user_id) with a class-level defined prefix in order to have a shorter field to get past a bug where the Test Student username was longer than 30 characters.

in doing so, applies the improved error message to mixins as well (previous commit only applied it to decorators)

changes failure on request.session.get('LTI_LAUNCH', None) returning None from an AttributeError to an ImproperlyConfigured exception

Remove apparently unneeded INSTALLED_APPS setting, as well as the LTI_CUSTOM_ROLE_KEY setting.  Update middleware to use hasattr instead of getattr.  Update tests to set the LTI_CUSTOM_ROLE_KEY django setting with a context manager block in each required test.

Add a script to run unit tests within auth_lti package.  Add a tests package with a few tests of the custom role key merge that is being added as part of this feature branch.  Filter out any empty roles from the merged list.  Update requirements in setup.py to remove unused django-filter and to include mock as a test requirement.  Remove *.html from MANIFEST as there are currently no html files.  Add .egg to gitignore.

Add a check for a custom role key - specified via an optional project parameter - and merge into the existing list of roles if present.

Add a new base mixin for LTI views that has two convenience methods for pulling params from session.  Add full_name as a stored session variable.

moved the code that stashes the LTI launch params to be after login(); fixes issue with masquerading in Canvas

Make corresponding mixin for LTI roles being required.  Remove GroupRequiredMixin and LoginRequiredMixin since the former is not used in LTI requests and neither was being used currently anyway.  Require django_braces with this library and use it's LoginRequiredMixin instead.  Update version.

when authenticating the user, put all of the LTI launch params into a dict called LTI_LAUNCH in the session

middleware will process all LTI launch requests, regardless of whether or not the user is already logged in.

when extracting the userid from the LTI launch request, look for lis_person_sourcedid first, then custom_canvas_user_login_id, then user_id