Created by: inmarelibero

This PR aims to let the user choose a number of columns up to 24, keeping the default to 12.

Column width of fixed and fluid layout are calculated in mixins.less, through grid.less and (optional) responsive.less

The final objective is to be able to build a fully working fixed/fluid layout with a custom number of columns (between 1 and 24, with 12 as default) only editing variables in

variables.less