Added Browser Action

This commit introduces the basic UI of the extension. The Facebook logo (downloaded from Facebook's brand website) is used as a clickable button on the browser toolbar. The image for this icon is included in both 1x (19x19) and 2x (38x38) resolutions in order to support the growing use of high-density displays. The bare basics of a manifest file is also introduced, as it is neccessary for configuring UI.
Logo and Icons

* updated .gitignore to exclude XCF versions of icons as well as the full-res logo
* added 128x128, 48x48, and 16x16 icons
* added icons to manifest.json
* updated website information in manifest.json
Main Functionality

* added core functionality of extension
* updated permissions in manifest.json (as well as a couple of other minor fields)
* added a copy of the MIT license with disclaimer about Facebook logo
License

updated Facebook properties disclaimer in the license document
extension ready for initial public release
README

updated README.md to reflect that app is no longer under development