Add autoprefixer-rails to the frontend

As discussed with @novotnyjakub this will later belong to ***mas-assets***.
@aduggin feel free to add the set of rules in this branch.

[AL D]: I've checked the default configuration and the following browsers are supported which is inline with our browser support:
 
Browsers:
  Android: 4.1, 4, 2.3
  Chrome: 31, 30
  Firefox: 26, 25, 24
  IE: 11, 10, 9, 8
  iOS: 7, 6.1
  Opera: 17, 16, 12.1
  Safari: 7, 6.1

Looks good to go: @andrewgarner