Moved vendored scripts over to using Bower for package management
Added Spin.js to Bower dependencies
Added Spin.js to popup's script tags
Cleaned up sass files a bit more, removed outlines from links

Prevents the Add Timer button from having a border around it when the
popup loads.
Added asynchronous message handling to the background page application class, so that the popup doesn't need to call functions on BackgroundApplication directly anymore
returning true from message handler whenever an AJAX function is called to make message passing work asynchronously
Switched popup over to using message passing instead of calling functions on the background application
Cleaned up and fixed image path in options page stylesheet
Added loading spinner to footer of timesheets table
Added additional visibility variable for form spinner
Table spinner is correctly positioned, showing and hiding when it's supposed to
added listen gem to dependencies
Added project:watch thor task to auto-compile assets
Styled and positioned form spinner. working as expected