Fixed issue #8161: (quexml-pdf) field lengths

Dev: multi-flexi array text and number questions now honor
Dev: maximum_chars attribute.
Dev: Short free text question: when no maximum_chars value
Dev: is given in attributes, field length defaults to 25, with values
Dev: values above 50 (two lines of text), a text box will be used
Dev: instead of the "form-type" text field.