Less variables to be used with media queries

LESS breakpoints

// Breakpoints
// ------------------------- Source: http://blog.scur.pl/2012/06/variable-media-queries-less-css/
@highdensity: ~"only screen and (-webkit-min-device-pixel-ratio: 1.5)",
              ~"only screen and (min--moz-device-pixel-ratio: 1.5)",
              ~"only screen and (-o-min-device-pixel-ratio: 3/2)",
              ~"only screen and (min-device-pixel-ratio: 1.5)";
@mobile:      ~"only screen and (max-width: 529px)";
@tablet:      ~"only screen and (min-width: 530px) and (max-width: 949px)";
@desktop:     ~"only screen and (min-width: 950px) and (max-width: 1128px)";
@desktop-xl:  ~"only screen and (min-width: 1129px)";