Grunt preen and concat

Set up grunt with tasks for:
  * preen - deletes unused files from bower_components, configured in
      bower.json
  * concat - concatenates preened bower components, configured
      automagically from the preen config

It's worth noting that this setup assumes the order of files within a
package doesn't matter. This is usually true since we often include only
one file from the package.

package.json

@@ -0,0 +1,11 @@
+{
+  "name": "textsecure-chrome",
+  "repository": "https://github.com/WhisperSystems/TextSecure.git",
+  "version": "0.0.0",
+  "devDependencies": {
+    "grunt": "^0.4.5",
+    "grunt-contrib-concat": "^0.5.0",
+    "grunt-contrib-jshint": "~0.10.0",
+    "grunt-preen": "^1.0.0"
+  }
+}