Add client side testing

[djmgit]

Add client side automated testing for the extension. All the prime features of the extension should be checked, most importantly the generated URL of the page to which the extension redirects users.

Some of the frameworks which might be suitable for this work are

• sinon-chrome
• selenium

You are free to use whatever you think would be most suitable for the task. Finally add a test command to package.json and add a testing section with details in README.md

Note
This is not a first timers issue as the label suggests. If you are a beginner please find issues with labels difficulty/low or difficulty/newcommer

[PaliwalSparsh]

@djmgit Feels like we are moving in Phase 2 of development. Are we expecting newcomers to come up or can I work on it?