Single implementation for annotations and namespaces

[abargnesi]

With the changes in #100 we now officially have two implementations for annotations and namespaces.

BEL::Annotation + BEL::Namespace
This implementation accesses values from external resources files (e.g. .belanno, .belns).

BEL::Resource
This implementation accesses values from RDF data published by OpenBEL/resource-generator.

These two implementations need to be consolidated using the BEL::Resource module as the abstraction. They should be made to work with URLs, RDF Repositories, or another source.

Necessary refactor:

• BEL Script parser
• BEL::Language structs
• Evidence model (BEL::Model::...)