Move all google cloud related code into implementation folder

[biilmann]

This sets the scene for better supporting multiple implementations of the runtime layer.

[biilmann]

This PR restructures the code quite a bit to make it a bit more future friendly.

There's now an implementations folder within both the processor-queue dir and the processors dir.

The implementations in processor-queue is meant as the main runtime for handling pubsub messages, deploying cloud functions and setup up topics, subscribers and buckets.

The implementations folder in the processors dir is meant for the actual cloud functions. They should automatically get deployed by the main runtime's deploy functions.

The plugin will now detect any processors in the processors folder and setup event handling for them.

These changes affects how queues and topics are named, so before upgrading it's necesarry to do a fresh deploy of the functions/buckets/topics.

With this PR the WORKER_TOPIC environment variable also becomes optional and there's now a separate topic/bucket for each potential processor.