Handle function deletion in workers

[mattrent]

This PR adds the correct handling of the delete message for functions. Specifically, now the core sends a delete message to all workers when a function is removed, ensuring that the old code is not running on the platform after deletion.

Additionally:

• adds a new hash field to functions. This is calculated from the function's code, and identifies each invoke/update/delete command to ensure the correct version of the function is being targeted on workers;
• pushes the new code to workers when issuing an update command;
• extends the cleanup method on workers to target RawResourceStorage as well
• fixes a bug in the release of both core and worker, where node_ip was being ignored

This closes #70.