Update gulp and libraries

[caneruguz]

Purpose

Clean up the gulpfile and update libraries

Changes

• Replaced minifyCSS with cleanCSS
• added sourcemaps tool
• Create minified version of the base.css with sourcemaps
• Remove paths variable from gulpfile
• Clean up gulp file to make more readable

[sloria]

Will gulp build both the unminified and minified version? Unless I'm missing something, it looks like it's only going to build minified.

End-users (such as the OSF) should be using the unminified version; they are responsible for doing their own bundling and minification.

[caneruguz]

@sloria The task builds both versions, it builds unminified first then the minified. Both of them are available to devs, the minified is there just in case.

[sloria]

Ah ok. LGTM