Issue 116 - Front-end code improvement.

This is a pull-request for https://github.com/evanxd/travis-reporter/issues/116.
Doing some work to improve the `front-end` code.
* Pack `similar` functions and variables into same `Javascript file`.
* Complete the `comments` of functions and variables.
* Deleted unnecessary `main.js` file.
* Simply `adjust` the `structure` of existing Javascript files.