Make recently_edited_plots return consistent data

recently_edited_plots was returning a 3-tuple in some cases and a
4-tupe in others. Adding a null to make this more consistent for
downstream templates that call this function.

Reverses commit 01ca8bf55d70cde8af942a48f28e2271527a2c21
Merge pull request #131 from steventlamb/bug/crashing_profile_page

Make recently_edited_plots return consistent data