CI-based Unit and End to End Testing

Adds support for CI-based Unit and End-to-End testing #290 (closed)

Test cases covered

1. building the Extension
2. eslint
3. gulp build (covers babel transpilation)
4. loading extension in chrome browser
5. bootstrap tour
6. translation pattern creation, deletion and updation
7. blacklisting of words and websites
8. testing translation in google and wikipedia
9. time taken by the algorithm for adding translated DOMs into the webpage
10. count of newer DOMs added while the lazy loading process
11. hovercard operations - mark as learnt words, saved translations
12. testing Popup.html

Visual explanation on running the tests: Link

Visualisation using mocha: Link