Explicitly add Ruby dependencies to project via Bundler

closes #1220
- This uses Bundler to install Ruby dependencies to handle explicit
  dependencies in provisioned environments
- The initial Gemfile contains SASS dependencies (sass and bourbon gems)

Gemfile

@@ -0,0 +1,4 @@
+source 'https://rubygems.org'
+
+gem 'sass'
+gem 'bourbon'

Gemfile.lock

@@ -0,0 +1,15 @@
+GEM
+  remote: https://rubygems.org/
+  specs:
+    bourbon (3.1.8)
+      sass (>= 3.2.0)
+      thor
+    sass (3.2.12)
+    thor (0.18.1)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  bourbon
+  sass

Gruntfile.js

@@ -31,7 +31,8 @@ var path           = require('path'),
         '!config.js',
         '!CONTRIBUTING.md',
         '!SECURITY.md',
-        '!.travis.yml'
+        '!.travis.yml',
+        '!Gemfile*'
     ],
 
     configureGrunt = function (grunt) {