Log DB Queries

Hi everybody :)

This PR add query logging for OC .

 Why doing Query logging?
Sometime it's hard to discover why a problem happend. In OC, we log some things but often not enough to discover the problem.
In sqlite for example it's hard to tell what was executed
or in a mutulized host, you often don't have access to db logs (as i have on my host).
So for an easy debug i add query and param logging :)

The idea is not to have this always enable as it can be really verbose and can make bigger problem harder to see.

I used a flag as suggested by @tanghus as we don't want to have that enable by default in a production environment ...

What do you guys think?