feat(cashier): add slot channel

components/cashier/README.en-US.md

@@ -96,6 +96,9 @@ Scoped slot of captcha header
 </div>
 ```
 
+##### channel
+Payment channel area slot, which can be used to add payment channel special operations, such as adding a bank card
+
 #### Cashier Events
 
 ##### @select(item: {text, value})

components/cashier/README.md

@@ -95,6 +95,9 @@ Vue.component(Cashier.name, Cashier)
 </div>
 ```
 
+##### channel
+支付渠道区域插槽，可用于添加支付渠道特殊操作，如添加银行卡
+
 #### Cashier Events
 
 ##### @select(item: {text, value})

components/cashier/channel.vue

@@ -6,6 +6,7 @@
       <p class="choose-describe" v-if="paymentDescribe" v-html="paymentDescribe"></p>
     </div>
     <div class="choose-channel" :class="{active: isChannelActive}">
+      <slot></slot>
       <div class="choose-channel-list" v-if="isChannelShow || isSingle">
         <template v-for="(item, index) in channels">
           <md-cashier-channel-item

components/cashier/index.vue

@@ -35,7 +35,9 @@
             :channelLimit="channelLimit"
             :default-index="defaultIndex"
             v-on="$listeners"
-          />
+          >
+            <slot name="channel"></slot>
+          </md-cashier-channel>
         </div>
 
         <!-- Captcha -->