Restrict access to alias sub_type's of attribute

[qclassified]

Alias database can be corrupted in the following manner:

>>> a = Attribute('ipv4', '1.1.1.1')
>>> b = Attribute('ip', '1.1.1.1')
>>> a.uuid == b.uuid
True

>>> backend.drop()
>>> a = Attribute('ip', '1')
>>> b = Attribute('ipv4', '1')
>>> a.uuid == b.uuid
False

So, do not allow creating 'ip' attribute and other alias sub_types

[qclassified]

alias is removed in v0.7