Massive refactoring OctaveSession and OctaveExpression, for fixing some bugs and problems: - fix bug with unhandling error in Expression with plog commands - remove finalazing in OctaveExpression: handle output in parseOutput function and error in parseError - fix problem, when octave prompt comes BEFORE error message, and we ignore error or some internal command handle it. - simplify logic in OctaveSession::readOutput - add handling subprompt (octave print subprompt, when user write unfinished octave statement)

Differential Revision: https://phabricator.kde.org/D15841