Update Attribute + unit Tests.
- enum types are now implemented in a straightforward String array. 
- Fixed bug matching NULL values with ANY and STRING Type. 
- Updated Unit tests. 
- Added support for negative years, which are years B.C. 
- Changed IAttributes interface to more descriptive AttributeSource.
Moved Test_VRL to vrs commons. 
VRLUtil tests are in vlet test module.
Disabled local file URL checking for now.
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