changed references to "install/dependencies.txt" to pip's "requirements.txt"
Merge pull request #154 from qdonnellan/master

Change `dependencies.txt` to `requirements.txt`
Fixed sentry issue 17666209 grades.admin misconfigured
Merge branch 'master' of https://github.com/burke-software/django-sis
Added missing cancel.png image
Override some of django_ldap_groups to support DOMAIN\username syntax
Slop.
Added ability to display grades as a letter grade
[close-11564744]
Merge branch 'master' of https://github.com/burke-software/django-sis into develop