Soc2014 meta refactor upgrade flags get field

# Main API

get_fields(m2m, data, related_m2m, related_objects, virtual,
include_parents, include_non_concrete, include_hidden, include_proxy) -> (field, field, ...)

get_field(field_name, m2m, data, related_m2m, related_objects, virtual) -> field

# Cached properties for fast access
fields -> (field, field, ..)
concrete_fields -> (field, field, ...)
local_concrete_fields -> (field, field, ...)
field_names (field_name, field_name, ..)
is `get_model()` too simple?