Links to projects and profiles should open in the same tab

[noah-schechter]

We have a slight inconsistency in the way we handle links on the Notifications page. Links to incidents open in the same tab while links to projects (for example that might arise from a "You have been added to the project []" notification) open in new tabs. Ideally, both types of links should open in the same tab. I imagine this has to do with our handling of external links—let me know if this change would cause other inconsistencies.

[noah-schechter]

This also applies to links to user profiles in comments, ie "@noah updated X", displayed in feeds (on the homepage or profile page).