[web] Allow breaking words in robotext

Test Plan: Log in as a user with long username, open private thread and check if the text is broken and that the page content isn't scrollable horizontally.

Reviewers: ashoat

Reviewed By: ashoat

Subscribers: KatPo, zrebcu411, Adrian, atul, subnub

Differential Revision: https://phabricator.ashoat.com/D887