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.

[Screenshot of size logging no warnings][2]
[Screenshot of error in middle of tests][3]
[Screenshot of tests success but warning][4]

[Screenshot of warning + file size from real code][5]


  [1]: https://github.com/gruntjs/grunt-contrib-cssmin#report
  [2]: http://puu.sh/6swtY.png
  [3]: http://puu.sh/6syB4.png
  [4]: http://puu.sh/6syuM.png
  [5]: http://puu.sh/6s0T5.png