Fix #2047

This pr updates all of the places that previously referenced the field or it's format of an aggConfig or table directly; now, they use the objects'  `#field()` and `#fieldFormat()` accessors.

This allows us to return different formatters based on the agg type, which currently prevents us from formatting counts as ip addresses (#2047).

@rashidkpc @simianhacker @w33ble @lukasolson, please keep this in mind when working with agg results in the future.