Run ActiveRecord's quoting machinery

Date, DateTime and Time objects are always converted to the format acceptable by BigQuery with this change.
This change also disables the actual quoting of strings - this is not needed as the JSON serializer does this.

@michelson, I was also thinking about a small optimization - we can skip running Base::quote() in line #89 for values that are strings (and maybe other types too). The code is clearer now and harmonised with ActiveRecord's flow, but does unnecessary things.

Edit: I've just added a second commit - BigBroda doesn't work with the newest ActiveRecord, this change fixes it.