feat(sortable): add functionality of using sortable inside sortable

[nchizhov]

Is it possible to use sortable inside sortable?

For example, this variant not working for me:

<template #childItemTemplate let-item="item" let-index="index">{{item.value}}</template>

<template #itemTemplate let-item="item" let-index="index">
  {{item.value}}
  <bs-sortable [(ngModel)]="localItems[item.initData.id]"
               [itemTemplate]="childItemTemplate"
               fieldName="name"
               itemClass="sortable-item"
               itemActiveClass="sortable-item-active"
               wrapperClass="sortable-wrapper">
  </bs-sortable>
</template>


<bs-sortable [(ngModel)]="globalItems"
             [itemTemplate]="itemTemplate"
             fieldName="name"
             itemClass="sortable-item"
             itemActiveClass="sortable-item-active"
             wrapperClass="sortable-wrapper">
</bs-sortable>

[valorkin]

sortable is highly a expiremental feature
so our plan is to split it in:

• drag and drop
• sortable list
• sortable tree

timeline? I wish I knew ;)