chore: Loading placeholders (#2322)

* Improve visual of loading mask

* Normalize placeholder naming

* Remove unused file

app/components/PlaceholderDocument.js

@@ -0,0 +1,29 @@
+// @flow
+import * as React from "react";
+import styled from "styled-components";
+import DelayedMount from "components/DelayedMount";
+import Fade from "components/Fade";
+import Flex from "components/Flex";
+import PlaceholderText from "components/PlaceholderText";
+
+export default function PlaceholderDocument(props: Object) {
+  return (
+    <DelayedMount>
+      <Wrapper>
+        <Flex column auto {...props}>
+          <PlaceholderText height={34} maxWidth={70} />
+          <PlaceholderText delay={0.2} maxWidth={40} />
+          <br />
+          <PlaceholderText delay={0.2} />
+          <PlaceholderText delay={0.4} />
+          <PlaceholderText delay={0.6} />
+        </Flex>
+      </Wrapper>
+    </DelayedMount>
+  );
+}
+
+const Wrapper = styled(Fade)`
+  display: block;
+  margin: 40px 0;
+`;