Add (failing) test for double-duplicate question
use shallow clone instead of deep clone

see
https://github.com/mwhite/Vellum/commit/495710437c5735e3312caceee70aca8860027bc8#commitcomment-7258430

Update by dmiller:
Thought this might fix the copy-of-copy issue (see failing test). It does not. Incidentally, jQuery's deep copy copies non-plain objects by reference, not deeply.
https://github.com/jquery/jquery/blob/10399ddcf8a239acc27bdec9231b996b178224d3/src/core.js#L165
Preserve itext object type on unlink

itext was deep-copied, and therefore it changed from being an instance of ItextItem to a plain object, which subsequently was not copied properly when duplicating a question.
Merge pull request #231 from dimagi/130785-double-dup

Fix itext bleed on copy of copy