WikiaSQL comments

@Wikia/platform-team 
https://wikia-inc.atlassian.net/browse/PLATFORM-404
@macbre - a comment in the form ```"# class::method\n``` will now be added to every sql statement automatically, ex:

```sql
# FooClass::barMethod
SELECT column1
FROM tbl
WHERE col1=5
```

Additionally, this introduces ```WikiaSQL->addComment()```, which can be used to add arbitrary comments to the sql output.