add LinkTransformer

add LinkTransformer classes and ResourceLinkTransformer

add interface and NullLinkTransformer

add MockLinkTransformer

add ResourceLinkTransformer

take into account arbitrary resource data elements

fix naming

wire LinkTransformer into Relation

use setter injection; remove references from ApiTraverser

remove unneeded class
fix naming
Merge pull request #11 from easybiblabs/topics/link-transform-cross-origin

add LinkTransformer for cross-origin link munging