Features/issue 546 less variables

[cognivator]

Proposed fix for setVariables Filter not resolving LESS variables (i.e. with "@" prefix) properly. ( #546 )

Modified the RegExp expression in this source in setVariables,

      angular.forEach(sortedVariables, function(variable) {
        str = str.replace(new RegExp('\\$' + variable.name, 'g'), variable.value);
      });

to this,

      angular.forEach(sortedVariables, function(variable) {
        str = str.replace(new RegExp('\[\$\@]' + variable.name, 'g'), variable.value);
      });

Created new specs for the angular unit tests.