feat: reordering documents in collection (#1722)

* tweaking effect details

* wrap work on this feature

* adds correct color to drop cursor

* simplify logic for early return

* much better comment so Tom doesn't fire me

* feat: Allow changing sort order of collections

* refactor: Move validation to model
feat: Make custom order the default (in prep for dnd)

* feat: Add sort choice to edit collection modal
fix: Improved styling of generic InputSelect

* fix: Vertical space left after removing previous collection description

* chore: Tweak language, menu contents, add auto-disclosure on sub menus

* only show drop-to-reorder cursor when sort is set to manual

Co-authored-by: Tom Moor <tom.moor@gmail.com>

app/components/Sidebar/components/DropCursor.js

@@ -0,0 +1,42 @@
+// @flow
+import * as React from "react";
+import styled, { withTheme } from "styled-components";
+import { type Theme } from "types";
+
+function DropCursor({
+  isActiveDrop,
+  innerRef,
+  theme,
+}: {
+  isActiveDrop: boolean,
+  innerRef: React.Ref<any>,
+  theme: Theme,
+}) {
+  return <Cursor isOver={isActiveDrop} ref={innerRef} />;
+}
+
+// transparent hover zone with a thin visible band vertically centered
+const Cursor = styled("div")`
+  opacity: ${(props) => (props.isOver ? 1 : 0)};
+  transition: opacity 150ms;
+
+  position: absolute;
+  z-index: 1;
+
+  width: 100%;
+  height: 14px;
+  bottom: -7px;
+  background: transparent;
+
+  ::after {
+    background: ${(props) => props.theme.slateDark};
+    position: absolute;
+    top: 6px;
+    content: "";
+    height: 2px;
+    border-radius: 2px;
+    width: 100%;
+  }
+`;
+
+export default withTheme(DropCursor);