Added keyValues for addFramedVertex with class type

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feat(internal): Added keyValues for addFramedVertex with class type

Added the function `<T> T addFramedVertex(final Class<T> kind, final Object... keyValues)`
 as a way to add key values to vertex elements. This includes tests for this new function.
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Fixed a bug that caused exceptions in the case of a vertex property with a cardinality other than single

Allow the value to a setter to be null

Fixed a bug that caused exceptions in the case of a vertex property with a cardinality other than single

Updated to not throw when returning a single item (this can just return null as frames did) and added a test

This simply unlinks the vertex in the case where the passed in vertex is null. This is similar to the frames behavior.

add information about support JanusGraph

ISSUES CLOSED: #27

ISSUES CLOSED: #21

More unit tests and fixes bringing coverage higher.