Support for Vendor name entity

Noteworthy: 
1.
I put some methods into `util/name_entity.rb` that will be shared between `Vendor`, `Customer`, and `Employee` (I am doing this entity next) and perhaps some other named entities. 

See:
```
   include NameEntity::Quality
   include NameEntity::PermitAlterations
```

In this PR, `Customer` was modified to have these methods mixed in (see `lib/quickbooks/model/customer.rb`), which I covered in the specs.

2.
Sparse update is not available for `Vendor` (see `lib/quickbooks/service/vendor.rb`).