Add groups for items

[BingBlog]

1、Some form may be need to separate to several groups, and has its own tips、group name;
2、�In some situations, we want to put some item together inline;

solution:

// config structure with groups
[
    formItem,
    group,
    formItem,
    group
]

// config for group
{
    group: true, // use to identify it is a group
    label: 'group name', // default ''
    inline: true,  // default false
    groupItems: [
        groupItem,
        groupItem
   ]  
}