Revamp the inputMethodQuery for konsolepart.

1. Surrounding text does not make sense for terminal, because
   surrounding text is used by input method for text predication, usually
   used together with deleteSurroundingText (commitString with negative
   offset), which is impossible for terminal application because it
   requires directly modify the buffer. Return value for surrounding
   text may cause invalid expectation from input method, e.g. input
   method may wrongly treat the command prompt as a part of text in the
   text buffer.
2. Fallback inputMethodQuery to QWidget default implementation, this
   allows ImHint to use QWidget::inputMethodHints().
3. Set default input method hints that makes sense for terminal.