fix and simplify learning outcomes in selective content import

the current learning outcome selection only occurs during course copy,
and will not bring in any outcomes that are in a group

in the future, we would like to add detailed item selection to the
dialog, but for now, make a simple solution that at least works

test plan:
* for both course copy, and course export/import, confirm that
 the 'select content' option gives you a checkbox to either bring
 in all the learning outcomes (and their groups) or none of them

fixes #CNVS-7464

Change-Id: I06a423ea949442cbba1459e04154681b6b2859bc
Reviewed-on: https://gerrit.instructure.com/33031
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Nathan Rogowski <nathan@instructure.com>
Product-Review: Hilary Scharton <hilary@instructure.com>