fix(spritesmith): split spritesheets in to multiple files to remove the

blurry iOS issue. Fixes
https://github.com/HabitRPG/habitrpg/issues/2510, see
http://goo.gl/IwxdI4 . Note, this commit isn't smart/dynamic, there's
commented-out code for handling dynamic splitting, but I couldn't get it
working - static 4 sheets for now

package.json

@@ -17,7 +17,8 @@
     "grunt-contrib-cssmin": "~0.8.0",
     "grunt-browserify": "~1.3.1",
     "grunt-contrib-clean": "~0.5.0",
-    "habitrpg": "git://github.com/HabitRPG/habitrpg.git#develop"
+    "habitrpg": "git://github.com/HabitRPG/habitrpg.git#develop",
+    "image-size": "~0.3.2"
   },
   "scripts": {
     "test": "mocha"