add link to student's text popups on the texts matrix

[davewhiteland]

Currently when investigating texts on the matrix, when the text pops up, might be handy to have a link there for sharing with other staff, because there is a unique URL to this user's texts (for logged-in staff) — it's the same one we're using in the text-authors page.

URLs to a student's specific text works like this (which opens the text on the admin "show user" page):

https://demo.buggyrace.net/admin/user/30#task-0-get
https://demo.buggyrace.net/admin/user/unity#task-0-get

Feels like this would be useful for sharing texts in staff-to-staff messaging.

[davewhiteland]

This was proposing a mistaken solution: link icon should be on the target (that is, the text's title) not the modal that is linking to it: especially since the URL required is on that modal already: it's the target of the button