Major refactor

Merge pull request #6 from mornir/dev

Refactor and more consistency between last visit an streak

Initial release 🤗

The web extension is now available on the Chrome Web Store: https://chrome.google.com/webstore/detail/track-it/kjdclicjmhibgokfflkhfccdillnkfbk
It is currently unlisted because I want to test it more and get some feedback.