[tcpServer] Updated to new sockets API

Based on https://github.com/GoogleChrome/chrome-app-samples/pull/205, I've updated the tcpServer sample to use the `chrome.sockets` API.
In this PR, on top of what was already done, the `hello_world.png` file has been removed,  the `README.md` file updated, `manifest.json` file version bumped and URLs updated as well to reflect the use of the new library and the `webview` now fits nicely in the window.

This PR also fixes an long-time issue when data is sent too early. See https://github.com/GoogleChrome/chrome-app-samples/issues/82