perform scanning in a worker, fixes #7

[mozfreddyb]

This will fix #7 and moves all scanning into a worker scanworker.js:
I had to change rules.js so that it doesn't require ScanJS to be loaded in the same scope (it's in the worker now!). We might want to solve this differently, if you guys don't like the current workaround.

I hope this request doesn't break pull request #42, otherwise I can happily rebase either.

[pwnetrationguru]

Looks like this can't be automatically merged into master after merging #42, so if you don't mine to fix conflicts and I'll review :)

[pwnetrationguru]

Also, just curious, does this now provide a loading animation while its running?

[mozfreddyb]

Hm no. Do you think we should show a throbber while the worker is busy?
I should be able to introduce this, when I repair this branch.

[pwnetrationguru]

Yah! A throbber would be awesome.

Below is currently how our testing framework mocha does it, and I REALLY like it. Would also allow a user to start navigating finished files before scan is done. Might be a little bit more difficult so we could break it up into a separate PR. If you want to include it in this one, I'm totally good with that as they are related.

What do you think of throbber in the header below?

[mozfreddyb]

I don't think percentage makes sense, as we have J of N files, and it should be a few seconds only. But a throbbler on the top right still makes sense, as well as the number of failures (we can't really measure failures).

I think we should do this in a different pull request though. I'm not really good with UI things and I'm unsure about how to tackle this right now. If you feel condifent, I'd actually prefer if you take a look at it, is that OK? :)

[pwnetrationguru]

@mozfreddyb, sounds good.

Let's just get the worker things merged in, and I can deal with a throbber in the UX uplift! :)

[pwnetrationguru]

from what I can tell, this lgtms 🐔