smarter linking of public portfolio owner's name

fixes CNVS-5352

only link to a user page if one is visible to the person viewing the
page. prefer the /about/:id page if the account has profiles enabled.
otherwise, prefer the /users/:id/profile page when viewing my own
portfolio and the /users/:id page otherwise (and only if permitted).

test-plan:
  - have a target user with a student enrollment
  - create a public portfolio for the target user

  - enable profiles on the account
    * log out and view the portfolio
      - the portfolio owner's name should not be linked

    * log in as portolio owner and view the portfolio
      - the portfolio owner's name should be linked to /about/...
      - following the link should be authorized

    * log in as an account admin and view the portfolio
      - the portfolio owner's name should be linked to /about/...
      - following the link should be authorized

    * log in as a teacher in the student's class and view the portfolio
      - the portfolio owner's name should be linked to /about/...
      - following the link should be authorized

    * log in as an unrelated non-admin user (i.e. student from some
      other class) and view the portfolio
      - the portfolio owner's name should not be linked

  - disable profiles on the account
    * log out and view the portfolio
      - the portfolio owner's name should not be linked

    * log in as portolio owner and view the portfolio
      - the portfolio owner's name should be linked to
        /profile
      - following the link should be authorized

    * log in as an account admin and view the portfolio
      - the portfolio owner's name should be linked to /users/...
      - following the link should be authorized

    * log in as a teacher in the student's class and view the portfolio
      - the portfolio owner's name should not be linked

    * log in as an unrelated non-admin user (i.e. student from some
      other class) and view the portfolio
      - the portfolio owner's name should not be linked

Change-Id: I812076d10bd3c56b87938627c9f095a1793128e6
Reviewed-on: https://gerrit.instructure.com/39863
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: August Thornton <august@instructure.com>
Reviewed-by: Rob Orton <rob@instructure.com>
Product-Review: Brian Palmer <brianp@instructure.com>