This way we get rid of object related content in resource.py and we can
finally move it to core/ in next commit.
Change-Id: Ia5b861115ae3ae1b90149863c4265dcc730b8cd4
This way we benefit from:
* knowing which attributes are used/required by each object class and
subclass
* Having validation function definitions near the class going to use them
Change-Id: I8fd6773c51d19405a585977af4ed72cad2b21db1