show eportfolio share link to owners

it could be confusing for some people to know to copy the underlying
link, since it wasn't being explicitly shown.

fixes CNVS-17631
closes gh-64

test plan:
- create an eportfolio
- it should show you an explicit link you can use to share it

Change-Id: I30da3b3a2ac74b08b9b4724739c11a883ffe3296
Reviewed-on: https://gerrit.instructure.com/46192
Reviewed-by: Benjamin Porter <bporter@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Sean Lewis <slewis@instructure.com>
Product-Review: Simon Williams <simon@instructure.com>