Added the SimpleBrowser demo for Linux.
Added Linux support to TChromiumWindow.
Removed unused code and added more code comments to the SimpleBrowser demos for Windows.
- Modified CefPostTask and CefPostDelayedTask to return a boolean value.
- Added CefCurrentlyOn helper function.
- Replaced all "CEF3" mentions by "CEF".
- Updated the OnBeforeClose event in all demos using TChromiumWindow to send a WM_CLOSE message instead of calling "close".
- Fixed all MDI demos. Now the demo will not close automatically when the last browser is closed manually.