Add EmptyState component

ts/components/conversation/media-gallery/EmptyState.md

@@ -0,0 +1,5 @@
+```js
+<div style={{position: 'relative', width: '100%', height: 300}}>
+  <EmptyState label="You have no attachments with media"/>
+</div>
+```

ts/components/conversation/media-gallery/EmptyState.tsx

@@ -0,0 +1,29 @@
+/**
+ * @prettier
+ */
+import React from 'react';
+
+import * as Colors from '../../styles/Colors';
+
+interface Props {
+  label: string;
+}
+
+const styles = {
+  container: {
+    display: 'flex',
+    justifyContent: 'center',
+    alignItems: 'center',
+    flexGrow: 1,
+
+    fontSize: 28,
+    color: Colors.TEXT_SECONDARY,
+  } as React.CSSProperties,
+};
+
+export class EmptyState extends React.Component<Props, {}> {
+  public render() {
+    const { label } = this.props;
+    return <div style={styles.container}>{label}</div>;
+  }
+}

ts/components/styles/Colors.ts

@@ -0,0 +1,4 @@
+/**
+ * @prettier
+ */
+export const TEXT_SECONDARY = '#bbb';