Recreating a challenge

[jmgasper]

From the Manage page mentioned in this issue (#191), the Recreate Challenge button isn't working. It should:

• Removes the git tcx labels (Not all labels, just tcx_ ones)
• Removes the assigned user
• Deletes the association in the issues table (delete all records for the combination of issue ID, repo ID)
• Sets the tcx_OpenForPickup label in git
• Create the challenge, as if the ticket were newly created
• Assigns the User