Tiles 3

Goals of this rewrite:

- Simplifies the extension's scope to make it easier to maintain. Uses Chrome's bookmarks bar as the primary data source instead of managing the storage and synchronization of Tiles. This should resolve issues about missing or lost Tiles, which is a common complaint. Another major benefit to this change is that we no longer need toolbar button ("browser actions"), a shared background page, and custom inter-tab communication.
- Leverages [React](https://github.com/facebook/react) and [fluxible-app](https://github.com/yahoo/fluxible-app). These libraries provide a framework that helps organize the codebase into logical pieces:
    - Components: Tiles, TileGrid, TilesApp
    - Actions: loadPage, changeBackgroundColor, resetTileData, changeTileIndex
    - Data stores: TilesStore, ApplicationStore
    - Chrome integration helpers: storage, bookmarks
    - Utilities: getWebsiteColor (this is pretty much the only untouched code left over from Tiles 2)
- Changes some of the visual design:
    - I decided to drop the two-letter periodic table "abbreviations", and instead just shrink the font and wrap text. This came from user feedback.