Rewrite Translator documentation

After TINKERPOP-3028 and the removal of bytecode, the Translator section of the documentation is going to need to be rewritten more holistically. There won't be anymore translators in the GLVs since they will all produce ANTLR compliant Gremlin by default. You'll always be able to get that form. Need to wait for both of those things to be done though before this documentation can be written properly as it's not yet settled what the API will look like for GLVs to get that Gremlin string. Probably need to review the upgrade docs for translators too on the removal of bytecode to make sure what's written there makes sense