Implementation of multiline texbox with selection and vertical scrolling.

Implement the multiline textbox selection and scrolling 
* any portion of the text can be selected
* the text scroll vertically as necessary
* the selection is properly visualized per line.
* If a "word" is too long it will be wrapped on sub-word character. (as in any editor)

However:
I specialized the render function of the multiline textbox, there is pbly a way to have better perf.

And ... it should maybe be re-implemented using the scroll area, since a scrollbar is very handy for a scrollable text box.
However that's a design decision, let me know what you think...