Refactor extension background script

[jaydeepsingh25]

Currently the background script in the extension includes lot of functionality in a single file and the script is becoming unmaintainable. Idea is to modularize the code and break it into smaller parts so that it is easier to maintain and scale in future.

[jeffbl]

@jaydeepsingh25 is there more to be done on this, or is it covered by the existing changes?

[jaydeepsingh25]

resolved by PR #433