Mercury branch - all the changes and functionality we need to have Mercury skin working

DO NOT MERGE, THIS PR IS PART OF PROJECT MERCURY! 
@SQLReview - This is executed on every getArticle API request from mercury

## Query
```sql
SELECT /* MercuryApi::topContributorsPerArticle */  rev_user
FROM `revision`  
WHERE rev_page = '25880' 
AND rev_deleted = '0'  
GROUP BY rev_user 
ORDER BY count(1) DESC 
LIMIT 6;
```

## Sample result:
```
+----------+
| rev_user |
+----------+
|  4938291 |
|  6141641 |
|  3999052 |
|  5317736 |
|  1481893 |
|  5079375 |
+----------+

```
## Explain

```sql
mysql> EXPLAIN SELECT /* MercuryApi::topContributorsPerArticle */  rev_user  FROM `revision`  WHERE rev_page = '25880' AND rev_deleted = '0'  GROUP BY rev_user ORDER BY count(1) DESC LIMIT 6\G;
*************************** 1. row ***************************
           id: 1
  select_type: SIMPLE
        table: revision
         type: ref
possible_keys: PRIMARY,page_timestamp
          key: PRIMARY
      key_len: 4
          ref: const
         rows: 63
        Extra: Using where; Using temporary; Using filesort
1 row in set (0.00 sec)
```