textF :: F (TextRequest String) (InputMsg (Int, String))
textF is the basic fudget for displaying plain text on one or several lines.
InputMsg messages containing pairs of line numbers (starting at
0) and contents of a line
when the user clicks on it. Double-clicking indicates completed input
(see inputDoneSP for an explanation on completed input).
textF:
labelF, displayF, moreF, pickListF, ...