Add a CSS lint task

[ds125v]

I just noticed a typo in one of the less files. I thought this would have triggered an error on compile, though maybe it can only notice certain types of mistake.

Either way, we should lint our CSS to check nothing else slips through. Something else we can nick from upstream Bootstrap's gruntfile.

[jobyh]

If you're happy for me to do so I can put something in with the work relating to #140 ? Been a bit hectic lately but I'll see if I can finish up with that over the next couple of days. Also been looking for a solution to the issue with sourcemaps. I'll have a look at the upstream Bootstrap repo and snaffle from there as you suggest if that's cool with you?

[ds125v]

Yeah that would be great. I think there's a few things we could just cut'n'paste from their stuff, including CSS comb, CSS lint, their new RTL flipper, their dev/dist split, their CSS minification strategy, in fact if you see anything else cool while your digging through it then odds are we want it too.

[ds125v]

Oh, they just added an auto-prefixer too, that's handy.

[jobyh]

Okay - I'll implement the linter and have a rummage through to see what can be harvested :+1:

[ds125v]

Possibly relevant link. This compiles less and csslints it in one step, so you get errors about the originating file:

https://www.npmjs.org/package/grunt-lesslint