Restructured upgrade docs for 3.4.0
Restructured upgrade docs for 3.4.0

Moved all deprecation/removal sections under a single heading and retitled some of the sections. CTR

pluradj/incubator-tinkerpop,krlohnes/tinkerpop,apache/tinkerpop,robertdale/tinkerpop,apache/tinkerpop,robertdale/tinkerpop,apache/tinkerpop,robertdale/tinkerpop,krlohnes/tinkerpop,pluradj/incubator-tinkerpop,apache/tinkerpop,apache/tinkerpop,robertdale/tinkerpop,krlohnes/tinkerpop,apache/tinkerpop,apache/incubator-tinkerpop,apache/incubator-tinkerpop,apache/tinkerpop,apache/incubator-tinkerpop,krlohnes/tinkerpop,robertdale/tinkerpop,krlohnes/tinkerpop,pluradj/incubator-tinkerpop