Crop course cover photo uploads

[brylie]

Cover photos should conform to a design constraint, so that the course cards have consistent look.

User Story

As a learner I want to visually scan the course listings so that I can quickly get an idea of course offerings

Examples

Image cropping can be done via:

• CSS
• JavaScript (client or server)
• Server-side image processing library
• the end user, prior to upload

[brylie]

In the client side JavaScript category, there is a jQuery plugin called jCrop. Meteor integration via Meteor jQuery jCrop.

[brylie]

After discussion, we have determined to go forward with a CSS crop feature. At a later point, we can explore additional cropping options.

[brylie]

@nizyev will you please reference this issue from your pull request?