program: made program class responsible for clearing program

program is now called from New action to clear the program instead of
the edit box; new program clear function calls new program model (unit)
clear function; new program model clear function clears all the program
model data (line info, code, errors, and dictionaries) and signals that
program has been cleared (signal connected to edit box clear slot); new
dictionary and info dictionary clear functions added along with new
abstract info class virtual clear function

also corrected an issue where the code needed to capture the current
modified line in the edit box when the New action is selected; and
renamed the edit box recreating line member flag to ignore change since
it is now also used when clearing the text document