[ON HOLD] Support redis for duplicate cache

[jfberry]

Many users have redis already installed for MAD. This PR adds (optional) support to poracle to use this distributed cache as an alternative for the in-memory duplicate cache. This will mean that events that have been processed will be remembered through restarts.

To activate, change the database, cache setting to redis. The other settings should be self explanatory.

      "cache": "redis",                // can be 'memory' or 'redis'
      "redis": {
        "host": "127.0.0.1",
        "port": 6379,
        "user": null,                   // default redis installation is no user/password but localhost only connections
        "password": null,
        "prefix": null,                 // usually leave as null! prefix all keys with this string (multi instance)
        "database": null                // usually leave as null! select this database on startup (advanced)
      }

Initial testing has not shown a significant improvement using this, so this requires further investigation. Please contact me before testing