google-cloud-translate: Support input and output options, improve usability

[jamestharpe]

• Allow source language to be set by context (msg, flow, global, or str)
• Allow target language to be set by context (msg, flow, global, or str)
• Explicit support for source language detection
• Add setting to allow the output payload to be only the translation
• Allow specifying of full language name (e.g. "Spanish")
  • Language code still works
  • Language names determined based on local system language
• Fix error handling
• Fix spelling error

I was careful to maintain backwards compatibility with the existing node but did not test for it specifically.

[kolban-google]

Thank you James ... this is awesome!!! Thank you SO much for the contribution. I'll schedule a refresh on the npm package and the Node-RED repo pickup.