Sarina/port cohorts inst dash

Port the existing Cohorts functionality to the new instructor dashboard and a fair number of improvements:

- Student name now shows up instead of being blank in user table
- Better UX
  * CSS rules
  * divs instead of uls
  * button stylings match rest of instructor dashboard
  * Text (on buttons, and labels) match rest of instructor dashboard
  * Better spacing (divs around elements, etc)
- First pass i18n (lots more still needed)

To do this I made copies of the existing code so that the "legacy" functionality is uninterrupted.

You can view this on my sandbox: http://sarina.m.sandbox.edx.org/ Log in as the default staff user. The demo course is set up to use cohorts, and you can compare and contrast the new dash implementation with the legacy dash.

Necessary future work
* improved UX
* remove feature off of Legacy dashboard & outdated code out of the codebase
* i18n
* Added lots of `TODOs` within the code that need to be addressed, particularly, on visiting the "Cohorts" page the information should be immediately displayed, not gated behind an additional button (yuck!). My Javascript isn't good enough to figure out the best way to fix this.
* API level unit testing; javascript testing