Ability to filter rows & columns for admin views

[scarroll32]

• then export as CSV
• sort by fields
• Leaderboard needs a round filter
• A precanned top-n report for multi-challenges would also be useful (with parameters), eg:

SELECT 
l.row_num, 
p.name, 
p.email,
c.challenge, 
r.challenge_round, 
r.challenge_id, 
r.id 
FROM  
challenge_rounds r, 
challenges c,
leaderboards l,
participants p
WHERE c.id = r.challenge_id
AND r.challenge_id IN (31,28,40,39) 
AND r.id IN (47,55,57,56)
AND l.participant_id = p.id
AND l.challenge_round_id = r.id
AND l.challenge_id = r.challenge_id
ORDER BY 4,1