Use indices for TinkerPop Text Predicates

TinkerPop added its own text predicates [in version 3.4.0](http://tinkerpop.apache.org/docs/3.4.0/upgrade/#_text_predicates) with the goal to provide a unified API also for text searches across providers.
While JanusGraph already has its own text predicates, it makes sense for us to provide good support for these TinkerPop text predicates so users have a good experience with JanusGraph.
Right now we support the TinkerPop text predicates, but they cannot make use of any indices. We should try to use an index if possible.

A complete list of the TinkerPop predicates can be found [in the reference docs](http://tinkerpop.apache.org/docs/3.4.1/reference/#a-note-on-predicates).

The issue names no JanusGraph files, tests, or entry points. Start with the TinkerPop 3.4.0 text-predicate documentation and inspect JanusGraph's existing support for TinkerPop predicates and indices. Done means supported TinkerPop text predicates can use an index where possible.

Written by the indexing model from the issue text.