Logging file size and closure warnings

Added support for logging the file sizes of the file pre and post minification via https://github.com/gruntjs/grunt-lib-contrib

To opt in to reporting you use the same option definitions as other grunt libraries (eg [from cssmin][1]):

```
gcc: {
    build: {
        options: {
            compilation_level: "ADVANCED_OPTIMIZATIONS",
            warning_level: "VERBOSE",
            report: "gzip"//defaults: false, valid options false, 'min', 'gzip'
        },
        src: ["<%= pkg['short name'] %>.js"],
        dest: "dist/<%= pkg['short name'] %>.min.js"
    }
}
```

The other logging feature included is closure warnings will now be printed to console.

![enter image description here][2]


  [1]: https://github.com/gruntjs/grunt-contrib-cssmin#report
  [2]: http://puu.sh/6s0T5.png