Fix webview example for use with QtWebEngine.

When the QtWebEngine is used as a back-end we need to call
QtWebEngine::initialize() or the example will fail as OpenGL context
sharing needs to be enabled.

Task-number: QTBUG-42745
Change-Id: I27ffc4043f759470f4d40441e62de2ba10728a01
Reviewed-by: Caroline Chao <caroline.chao@theqtcompany.com>
Doc: Renamed the webview example

- Updated the subdirs project file referring the example
- Updated the examples page with the new name
- Moved the qtwebview-example group page to doc/src

Change-Id: I53ba49103ad2bfff21a230dded456be1e88231f2
Reviewed-by: Christian Stromme <christian.stromme@digia.com>
Fix the window title of the example.

Wire the window title to QWebView and set the application display
name. Qt will then automatically append it.

Change-Id: I327f0baa9ad5272691d84fd7eee3754b514daee6
Reviewed-by: Christian Stromme <christian.stromme@theqtcompany.com>