Adding features scan keys for duplicated values
Add skip_verify step in DOMM Parser, for easier testing

- This parameter will signify to Parser to not look for elements in
defined namespace
Separated tests into parts
Add test for duplicate tag type
Add type_to_name helper function
Add test for duplicated package names
Add _checked_add that verifies the there aren't duplicate elems
Add verifications for literal values
Rename test_enums to more meaningful name
Add test for duplicate slots in ValueObject