Make REST API return and accept model boolean attributes as true/false instead of 't'/'f'

[kazlauskis]

The REST API interface returns and accepts boolean values as 't' or 'f' instead of true or false. To differentiate these values from regular text attributes, clients need to maintain a list of all the warehouse core boolean attributes and convert them from 't' or 'f' to true or false when communicating with the warehouse.