Add rails controller logging

This adds time spent in GC to Rails controller logging, for example:
```
Completed 200 OK in 631ms (Views: 22.1ms | ActiveRecord: 18.7ms | GC=167.0ms | Search=0.0ms | Redis=2 | Memcache=7 | master-queries=3 | shard_0-queries=20 | shop_name=shop1.myshopify.io  | dest_host=shop1.myshopify.io  | pid=45776  | shop_id=1 | shard_id=0 | request_id=cfec5667-8f0b-4b11-b676-6300083bd04f | session_id=20ee8aefeeeae62ece61f6510eed6ac6446723cb315659084f760488bcac1857 | ssl=false | rev=1 )
```

@byroot, @arthurnn for review because Rails. Am I doing this right?

/cc: @camilo
You might want to put all the `/rails/*` stuff under that if.