support for porcupine v2

[asmirnou]

Support for the latest version of Porcupine.

The configuration section in profile.json should look like:

"porcupine": {
  "access_key": "<porcupine-access-key>",
  "keyword_path": "porcupine-keyword-file.ppn",
  "model_path": "porcupine_params.pv"
},

This PR is coupled with the following one: rhasspy/rhasspy-wake-porcupine-hermes#11

Until the PRs are merged, the latest porcupine in Rhasspy can be tested by compiling from sources as described here.