Some enhancements to the widget used to get player input for
getline() and also menu search and text window search.
give caller control of [cancel] and [okay] button names;
give caller a say in how wide the string input box should be
instead of basing that on the length of the prompt string
(needs more work...);
use fixed-width font for displaying the user's input;
clean up the widget layout a little bit.
src/Makefile needs a dependency update for Qt (not included).
