Minimal RAP port of SWT's StyledText widget.

The port has many limitations, including:

• the widget is read-only, text can only be displayed but cannot be modified
• many public APIs have not been implemented
• no performance optimizations for large texts
• needs RAP 1.5.x (not 2.0.0)

I am making it available here, because I am using it in some of my own projects.