Rewrite the sync daemon in go

[lucabrunox]

Two main reasons why I'd like to get rid of PHP:

1. Child processes are hard to manage, in general. They would be simply replaced by goroutines. There's no reason to use child processes for this kind of job.
2. Task queues are handled with PHP shared memory queues, that are hard to manage because the size of the message has to be estimated somehow.

If we want to add some more logic on how tasks are scheduled in PHP, it's going to be hard due to the issues listed above. A language with builtin concurrency like go would be very helpful instead.