(WIP) Ex-60 All students using registration codes from that purchase to be unable to access course material

@cdodge I am just sharing my understanding for this task as there are some statements on wiki page: https://edx-wiki.atlassian.net/wiki/display/UX/White+label%3A+Payment+due that are creating confusions. 
In this PR, I am implementing the scenario -> If a third-party is responsible for payment. 

@cdodge If students try to access the course via a direct link to course material then it is not possible to show the content that they saw last, and redirecting them from the "you were last in"  landing page with a modal popup. So I in case of direct access to course i am redirecting the user to dashboard. 

Kindly share your feedback & suggestions. 
(Note: Some questions were asked related to EX-60 on JIRA)

Thanks.