Update objects.py with review feedback
Update objects.py with review feedback

Make infoblox_type and return_fields as property.
Rename IPAllocationObject -> IPAllocation, ARecords -> ARecordBase,
_infoblox_object_type -> _infoblox_type.
Fixed several typos.

bondar-pavel/infoblox-client,arnaudcoquelet/infoblox-client,infobloxopen/infoblox-client