convert seletive content checkbox to radio buttons

fixes CNVS-9885

When you import or copy a course you are given the option to select the
content you want to import. The option to select this was a checkbox
but has now been changed to a radio button. This should help people who
are confused by the process or forget to check the selective content
button. Default should be selecting all content

Test Plan
1. copy a course by going to 'import content into this course' for the
course settings.
2. select the radio button 'select migration content'
3. it should still allow you to select migration content
4. select all content should be the default
5. Next..
6. Go to course settings and click on 'copy this course'
7. There should be two radio buttons now that say 'All content' and
select specific content.
8 The default should be 'All content'

Change-Id: I62c7161c621e6872048b04a5a2c0fe696adf316f
Reviewed-on: https://gerrit.instructure.com/31112
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Jeff Fox
QA-Review: Matt Fairbourn <mfairbourn@instructure.com>
Reviewed-by: Jeremy Stanley <jeremy@instructure.com>