[Enhancement] Fetch previous messages in the conversation (#355)

* Fetch previous messages in the conversation

* Add specs for conversation store

* Fix codeclimate issues

* Exclude specs folder

* Exclude globally

* Fix path in exclude patterns

* Add endPoints spec

* Add snapshots for Spinner

* Add specs for actions

app/javascript/shared/components/Spinner.vue

@@ -0,0 +1,67 @@
+<template>
+  <span class="spinner small"></span>
+</template>
+
+<style scoped lang="scss">
+@import '~widget/assets/scss/variables';
+
+@mixin color-spinner() {
+  @keyframes spinner {
+    to {
+      transform: rotate(360deg);
+    }
+  }
+
+  &:before {
+    content: '';
+    box-sizing: border-box;
+    position: absolute;
+    top: 50%;
+    left: 50%;
+    width: $space-medium;
+    height: $space-medium;
+    margin-top: -$space-one;
+    margin-left: -$space-one;
+    border-radius: 50%;
+    border: 2px solid rgba(255, 255, 255, 0.7);
+    border-top-color: lighten($color-woot, 10%);
+    animation: spinner 0.9s linear infinite;
+  }
+}
+
+.spinner {
+  @include color-spinner();
+  position: relative;
+  display: inline-block;
+  width: $space-medium;
+  height: $space-medium;
+  padding: $zero $space-medium;
+  vertical-align: middle;
+
+  &.message {
+    padding: $space-normal;
+    top: 0;
+    left: 0;
+    margin: 0 auto;
+    margin-top: $space-slab;
+    background: $color-white;
+    border-radius: $space-large;
+
+    &:before {
+      margin-top: -$space-slab;
+      margin-left: -$space-slab;
+    }
+  }
+
+  &.small {
+    width: $space-normal;
+    height: $space-normal;
+
+    &:before {
+      width: $space-normal;
+      height: $space-normal;
+      margin-top: -$space-small;
+    }
+  }
+}
+</style>