Update ListField.js

Allow object rows in Array on ListField (select), allowing to preserve insertion order instead of order by value.

Allows a data structure like this:

[{"text": "Aeronautica", "value": 18}, 
{"text": "Agricoltura - silvicoltura e pesca", "value": 1}, 
{"text": "Altre categorie non classificate", "value": 62}]

to be used in case of a list that must be displayed in a different order than "by value", e.g. when value contains a key and text the right alphabetical order.

![alpacalist](https://f.cloud.github.com/assets/2143851/1753345/36ba83e6-663b-11e3-8e08-c8cc5bd5f285.jpg)
Using an Array is the only alternative for this issue since even if json is served in the right order javascript reassign the order by key if a json object is used.