listnr_content_script.js and more: Open Tool from Listn directly

Extends this extension to inject code into listnr to support
opening this tool directly.

background.js: the "middle man" code to handle the request, launch the
tool, and pass in the feedback URL.

listnr_content_script.js: code injected into listnr.

manifest.json: New permissions to support this

popup.js: Code in the tool that can receive the feedback URL from
background.js. If tool is launched normally, this is dormant.

TEST=Manually tested in browser

Change-Id: Ibb34c8718e567369c7661b77d68c19a48f73ed4d
5 files changed