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.