Add basic web interface

[wvengen]

Scrapyd has a basic web interface. It would be useful to have something here too, for easy access.
Granted, you can already inspect everything with docker or kubectl, but a basic web interface still has its uses.

The idea is to have a simple interface:

• show projects, versions, spiders
• list jobs
• schedule and cancel jobs
• view job logs (after Expose logs #12)

[wvengen]

This can be very very simple.
SInce there is an API already, it does make sense to make use of it.
This means it would be a basic client-side application accessing the API. (Or add JSON and HTML responses to the API endpoints, if you can do that without polluting the API code, that may be an option. Don't over-engineer here.)
Don't use some large framework, but keep it small and simple.

[JeremyVriens]

Can we also use https://github.com/my8100/scrapydweb for this? If we're adhering to the same API contracts, I think this should work out-of-the-box for scrapyd_k8s as well.

[wvengen]

Well, yes, and no. That project is meant for multiple hosts running scrapyd, with possibly different environment. It would be nice if scrapyd-k8s would work nicely in that (that would be a different issue, perhaps, or maybe not). And it may be a bit overkill.

I was thinking of something a bit more light-weight, that would be something like what scrapyd offers, but a little nicer, and more tuned to scrapyd-k8s. I would think of it something like a client-side app, talking to the existing API, so except for some asset serving, it wouldn't actually involve more code in scrapyd-k8s core (or go real-time with a websocket connection, that's not possible with regular scrapyd servers, but that can quickly get complex).

The goal is that users can get an easy overview of what is happening with scrapyd-k8s, without having to setup more things.