(Linux) drag and drop file support in the editor

[portaloffreedom]

Drag and drop in the Editor is only supported on Windows at the moment

[turanszkij]

The windows implementation works like this:

1. enable drag and drop file application-wide with DragAcceptFiles(hWnd, TRUE);
2. parse WM_DROPFILES message from OS and retrieve file names with DragQueryFile() function
3. For each filename, call editor.renderComponent.Open(filename);
4. At the end set window to foreground for better user experience with SetForegroundWindow(hWnd);. Without this, application is in background and remains paused, so it looks as if file drop wasn't registered until user goes back to the window.

Maybe this will help linux implementation.