Various fixes and corrections

- Introduced possible option to enable C++11 support to the premake
  script. For now it is disabled as we do not need it after all.
- Disable sorting in the Treepopup.layout - we set the order by our
  selves
- Coboboxes - GetSelection lost constness
- Listboxes - Added HasItem method and support for double click events
- ScrollWidget - Added virtual destructor
- PushButtons - ConfigUpdate lost constness
Dynamic text widget support.

- Implementation of ScrollTextbox and CEGUITextbox classes.
FrameWindow extensions.

- Frame windows will have now an modality attribute.
- Added methods to find PushButtons and Textboxes attached to a window.
Implementation of Alert Popup.
Implementation of Confirm Popup.
File picker implementation.
Forgot the implementation of Frame Window modifs.
DialogManager extensions.

- Implemented a stack to track modal windows.
- Added support for AlertPopup
- Added support for ConfirmPopup
- Added support for Textbox widget
- Added support for FileDialog
Settings for syntastic and youcompleteme vim plugins.
Cleanup in external packages.