Makes the given group active
@param {Ext.Component} cmp The root component to make active.
function(cmp) {
        var me = this,
            newGroup = cmp,
            oldGroup;

        if(Ext.isString(cmp)) {
            newGroup = Ext.getCmp(newGroup);
        }

        if (newGroup === me.activeGroup) {
            return true;
        }

        oldGroup = me.activeGroup;
        if (me.fireEvent('beforegroupchange', me, newGroup, oldGroup) !== false) {
             me.activeGroup = newGroup;
             me.fireEvent('groupchange', me, newGroup, oldGroup);
         } else {
             return false;
         }
         return true;
    }