add Collapse component

add Collapse component

components/collapse/panel.vue

@@ -0,0 +1,57 @@
+<template>
+    <div :class="itemClasses">
+        <div :class="headerClasses" @click="toggle">
+            <Icon type="arrow-right-b"></Icon>
+            <slot></slot>
+        </div>
+        <div :class="concentClasses" v-show="isActive" transition="height">
+            <div :class="boxClasses"><slot name="content"></slot></div>
+        </div>
+    </div>
+</template>
+<script>
+    import Icon from '../icon';
+    const prefixCls = 'ivu-collapse';
+
+    export default {
+        components: { Icon },
+        props: {
+            key: {
+                type: String
+            }
+        },
+        data () {
+            return {
+                index: 0, // use index for default when key is null
+                isActive: false
+            }
+        },
+        computed: {
+            itemClasses () {
+                return [
+                    `${prefixCls}-item`,
+                    {
+                        [`${prefixCls}-item-active`]: this.isActive
+                    }
+                ]
+            },
+            headerClasses () {
+                return `${prefixCls}-header`;
+            },
+            concentClasses () {
+                return `${prefixCls}-content`;
+            },
+            boxClasses () {
+                return `${prefixCls}-content-box`;
+            }
+        },
+        methods: {
+            toggle () {
+                this.$parent.toggle({
+                    key: this.key || this.index,
+                    isActive: this.isActive
+                });
+            }
+        }
+    }
+</script>