expand id regex in getSubject (A-Fa-f -> A-Za-z)

getSubject() wasn't working on my mongo id 'ABS' because 'S' wasn't included in range A-F.

it's still not right because mongo identifiers can include other characters like -,/\

Seems like getSubject() should just pass whatever id is provided to the ModelManager methods and let them take care of validation.