Prepare it for Bootstrap 4 (SASS parser)

[elboletaire]

We need a SASS parser and a Sass helper to get everything working with Bootstrap 4!

I don't like the leafo's version (that's why I changed from leafo's lessphp to oyejorge's one), so let's try to find an alternative.

Here's a nice alternative:

• https://github.com/sensational/sassphp

[elboletaire]

After taking a look at new leafo's sass parser and knowing that the sassphp alternative linked above requires a php module compilation/installation I think that using leafo's version would be a good choice after all.

https://github.com/leafo/scssphp

It seems to be better coded and much more tested, making it a nice alternative.

If you take a look to leafo's lessphp parser and compare it with his scssphp parser you'll understand what do I mean.