Strip down demobrowser to become simplebrowser

Demobrowser changes:
* remove QLocalServer/Socket
* remove AutoSaver
* remove restoreLastSession
* remove general QSettings
* remove downloadManager
* remove bookmarkManager
* remove historyManager
* remove searchBar
* favor setStyleSheet over overriding paint methods
* use lambdas where suitable
* use QProgressBar instead of own painted widget
* use QToolButton instead of own painted buttons
* remove QStackWidget, use single UrlLineEdit per window
  instead of per tab
* split files to keep own classes: webpage and webview
* remove tracking windows by QPoiner
* remove WebPageActionMapper, TabBar classes
* remove QDrag dead code
* remove special OS X close app handling
* fix encapsulation, clean up application logic

Change-Id: I4849b6a2de739dea4f01229abdb90418601a2397
Reviewed-by: Kai Koehne <kai.koehne@theqtcompany.com>
Reviewed-by: Alexandru Croitor <alexandru.croitor@theqtcompany.com>