Fix priority value alignment for maproulette campaigns in assignments table

if I add a favorite to a MapRoulette Campaign, I get a right-justified `0` in my "Assignments Table" on my dashboard.

If MapRoulette Campaigns are added as favorites, they should show up in the "Assignments Table" on the dashboard with the same rules for rendering as TM campaigns.

@jvntf I believe this is related to the mapping of priority values to user favorites found here:

https://github.com/developmentseed/scoreboard/blob/develop/components/dashboard/DashboardAssignments.js
and
https://github.com/developmentseed/scoreboard/blob/develop/components/AssignmentsTable.js