Biggest change: Script injection to read <title> element for tab labels

Minor changes:
- Updated css: slightly better tabbed browser look-and-feel
- Bug fix: Select first tab during load
- Bug fix: location bar naming in Browser handlers
- Refactor tab handles to constist of <li><p>...</p><a>X</a></li>
Major change:
Implement open-in-new-tab and close-tab button correctly

Minor changes:
- CSS fix: only selected webview is visible
- Only need one webview message listener in the embedder
- Counter stored in TabList ensures unique tab names
- Order of state change + layout calls fixed in TabList.selectTab()
- Bug fix: Misspelled method(s) "detatch" -> "detach"
- Bug fix: this is that in Tab.initWebview()
- Marshall objects for message passing + use tab name in guest->embedder messages
New add-tab button