add save_imported_question option

to combined questiontype rather than base class
in 2.6 this code duplication will be removed when we
will be able to use save_question to save the import
data.
OU-6637 Fixing width of text input

when specified by syntax __{width}__
also added a phpdoc comment with improved
type hinting for text entry renderer sub class.
OU-6641 Fixed scoring

of ou multiple response subqs in
interactive mode with 'countback' scoring
OU-6640 changed the order of feedback

And took a look at the styling to fix the spacing
between the feedback elements.
OU-6639 changed num parts correct feedback string

and added different feedback when not plural