copy build tasks from theme

[mattstratton]

We will need all the properly updated build tasks from the theme.

These include:

• gulp
• updated appveyor
• updated travis (maybe; travis in the theme does a lot of different stuff)
• updated netlify configurations

We might be able to completely remove travis, and maybe just run htmlmin in the netlify step to check it there.

[mattstratton]

I prefer to keep travis in this repo the way that it is. No need to change it.

I think appveyor mostly already works, but I'll check.

gulp and netlify are the ones we need to do.

We can move gulp in advance; netlify is go-live time.

[mattstratton]

My plan for this is that right before go live, I am going to do a fresh clone of devopsdays-web, copy the theme into it, and then also all the gulp stuff. I'll do a gulp run locally to make sure there are no errors, and then this will all be part of the same PR. The deploy preview should, in theory, catch anything, although we have to be careful to not merge anything right while i'm doing this.

[mattstratton]

Resolved in #1998