InstantAnswer.pm - modify the structure of the updates column

@russellholt @jdorweiler @jbarrett 

As said in the Asana task, now the updates column will contain an array of hashes for each field.
Each time a user will make an edit, a new hash containing the new value and the timestamp will be added to the corresponding field array in the updates column.

This will make it easier to retrieve the last edit for each field in the upcoming current_status function (see the Asana task).
I'd pull the subexpression out to make it easier to read