Use actual colors in SASS variables. Rework of #1542.

[sgomes]

This PR replaces our color variables to use actual colors rather
than strings. It also updates the template generation and
customizer to use '#name' style placeholders instead of '$name',
so that CSSO doesn't complain about the syntax.

This PR may later be invalidated if we decide to move away from SASS,
but for now it provides a good baseline for current development.

@Garbee, @surma: PTAL!

[Garbee]

LGTM.

Looks like I can dump my local branch with the same import since this is doing the same thing correct? (I'm still like halfway through conflicts so, making sure before I dump the work.)

[sgomes]

Oops, sorry @Garbee, didn't know you already had a branch doing the same thing! Yes, this does the same thing as #1542, with the added support for gulp-csso 1.1, which doesn't like $variables any more.

[Garbee]

Don't worry about getting it done. I started the merge after our meeting the other week. But, there are a lot of conflicts so I was just slowly doing it as I had time. I was just doing the slow/hard way to try and keep the commit history.

Thanks for getting it done though, it is much needed.

[Garbee]

Restarted Drone on this one. Looks like a timeout occurred for some reason, didn't look like an actual failure of the build.

[surma]

Code LGTM. Drone is timing out. Restarted it. Let’s see.

[sgomes]

FYI: neither of you managed to restart Drone, even though I'm sure the UI seemed to indicate you did.

You're likely not logged in, like I wasn't, so even if the button is shown and you click it and it seems like something is happening, nothing actually is. You'll need to go to https://ci.cloudware.io/ and re-login. Sigh.