Feature: CSON support (#1305)

Adds CoffeeScript Object Notation CSON support in Web Essentials: https://github.com/bevry/cson

Addresses #1305. /cc @somecallmechief.

Following are the highlights:
* Content type.
* Used CoffeeScript icon.
* Menu items.
* Compilation.
  * CSON to JSON.
  * JSON to CSON.

Also, user can select multiple files in solution explorer and compile them at once. The corresponding option will be highlighted if one or more files with matching extension are available.

**TODO**

Compile on Save: (also need settings to make it disable) so the CSON or JSON files which has their counterparts available should be in sync on save.