add fileOpenDialog and enable loading of urdf from GUI

(will add .bullet file support soon)
Uses native Windows (getFileOpenFileName) and Mac OSX NSOpenPanel,
on Linux using pipe popen to zenity)

btgui/OpenGLWindow/Win32OpenGLWindow.cpp

@@ -137,6 +137,40 @@ void	Win32OpenGLWindow::endRendering()
 
 }
 
+int Win32OpenGLWindow::fileOpenDialog(char* fileName, int maxFileNameLength)
+{
+	//wchar_t wideChars[1024];
 
+		OPENFILENAME ofn ;
+	ZeroMemory( &ofn , sizeof( ofn));
+	ofn.lStructSize = sizeof ( ofn );
+	ofn.hwndOwner = NULL  ;
+
+#ifdef UNICODE
+	WCHAR bla[1024];
+	ofn.lpstrFile = bla;
+	ofn.lpstrFile[0] = '\0';
+	ofn.nMaxFile = 1023;
+	ofn.lpstrFilter = L"URDF\0*.urdf\0";
+#else
+	ofn.lpstrFile = fileName;
+	ofn.lpstrFile[0] = '\0';
+	ofn.nMaxFile = 1023;
+	//ofn.lpstrFilter = "All\0*.*\0Text\0*.TXT\0";
+	ofn.lpstrFilter = "URDF\0*.urdf\0";
+	
+#endif
+
+	ofn.nFilterIndex =1;
+	ofn.lpstrFileTitle = NULL ;
+	ofn.nMaxFileTitle = 0 ;
+	ofn.lpstrInitialDir=NULL ;
+	ofn.Flags = OFN_PATHMUSTEXIST|OFN_FILEMUSTEXIST ;
+	GetOpenFileName( &ofn );
+	return strlen(fileName);
+
+
+	//return 0;
+}