Update version to 1.4.3

What's new:

* Removed tabs permission from Chrome Web Store manifest file as it's not needed
* Fixed up web app icons for Android and iOS (apple-touch-icon)
* Added a link to the Chrome Web Store in the footer
* JSON export is now easier to read with new line characters after each comma
* Added a lot of comments and cleaned up the code formatting
* Refactored the showNewTasks() method