Logging function

[s-coimbra21]

Added a function that is called whenever an error occurs in a mutation or query. Whether it is a connection error or GraphQL error. It can be added like so:

@rootDataConnect({
  logging: ({data, errors}, dispatch) =>  console.log(`${errors}`)
})

data may not exist, it will be there if one of the queries returned some data but had GraphQL errors.
errors should always an array of objects which should always have a message key with a string.

[bruno12mota]

Fix the unit tests and it's ready to go ;)

[s-coimbra21]

Changed so that the logging function isn't kept in redux state (for obvious performance reasons). It must now be passed in the logging key of the rootDataConnect config for queries and in the mutation's options ({ fragments: {...}, logging: console.log}) for mutations.

[coveralls]

Coverage decreased (-0.1%) to 71.774% when pulling f49bc19 on s-coimbra21:loggingAPI into ea045ff on relax:master.

[bruno12mota]

Hey! Could you fix the conflicts so we can merge this?