Fix race condition when launching Oxide helper process

[thecrypticace]

Fixes #1519

We were calling startIfNeeded() but it did async work before assigning the connection which means if scan() is called once per project the flow looks like this:
Project 1-N: scan() -> startIfNeeded() -> check for existing connection -> await … -> setup connection -> done

Since projects are loaded via Promise.all(…) every single one will run all the way up to the await call, wait, fork a process, setup an RPC connection, and overwrite the this.helper and this.connection properties. I think the additional processes would stick around because of closure scopes but not 100% sure about that as they should've otherwise been unreferenced.

This PR changes the setup in a few ways:

• The code that looks for the Oxide helper async is gone. The relative path is resolved at startup.
• We synchronously store a promise to the object containing details to access the helper process
• Most of the process is now synchronous with a small promise that waits for the process to become ready.