Grunt speed and performance

Use [shootaroo/jit-grunt](https://github.com/shootaroo/jit-grunt) to load tasks.
Comparison between `grunt (default)`
Before
![before](https://cloud.githubusercontent.com/assets/5230079/4325636/2fc77782-3f67-11e4-8b1a-d2930447fc6d.jpg)
Now
![now](https://cloud.githubusercontent.com/assets/5230079/4325643/3e7ec7ee-3f67-11e4-9683-512bfdf1ed82.jpg)