update "choose home page" dialog

test plan:
 0. BEFORE APPLYING THIS CHANGE SET,
    create a course, enable draft state, do not create a
    wiki front page, use the *old* "Choose Home Page"
    dialog, select "Pages Front Page", and save
 1. NOW APPLY THIS CHANGE SET.
    open the new "Choose Home Page" dialog, and confirm
    that "Front Page" is grayed out and disabled,
    and "Recent Activity Dashboard" is selected
 2. create a new course and enable draft state
 3. go to the course home page and click "Choose Home Page"
 4. the new dialog should appear and should contain
    a radio button for each page selectable as home page.
 5. note the "Front Page" radio button should be disabled
    since there is no home page.
 6. click the link next to the disabled radio button
    labeled "Front page must be set first". It should take you
    to the "Pages" page, where you can create a page and set it
    as the front page.
 7. Return to the course home page and click "Choose Home Page"
 8. Now the "Front Page" radio button should be selectable
    and the page title should appear next to it
 9. Click the "Change" link and verify it takes you to the
    Pages page
10. Confirm that all the other radio buttons work as expected also

fixes CNVS-10987

Change-Id: I056f91015af6f998b3018ec9bd31b98d6848bc3f
Reviewed-on: https://gerrit.instructure.com/35260
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Bracken Mosbacker <bracken@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>
Product-Review: Hilary Scharton <hilary@instructure.com>