deps: react-bootstrap 0.31 -> 2 (Bootstrap 5 CSS deferred as debt)

Removes the largest batch of React-19-blocking warnings: the 0.31
components (Grid, FormGroup, ControlLabel, Navbar.Header/Brand, Checkbox,
SafeAnchor) all leaned on legacy context / defaultProps.

29 files converted: Grid->Container, FormGroup/ControlLabel/FormControl/
HelpBlock -> Form.Group/Label/Control/Text, Checkbox -> Form.Check (label
as prop), bsStyle->variant (default->secondary), bsSize->size,
pull-right->float-end. Custom Col.js now re-exports v2's Col; custom
NavItem.js rewritten self-contained (no SafeAnchor/createChainedFunction);
Navigation.js drops react-bootstrap Navbar (raw markup anyway).

CSS stays on Bootstrap 4 (alexwine:bootstrap-4) for now: the BS4->5 jump
is entangled with the jQuery carousel/swipe + navbar-collapse and is
tracked as separate debt in UPGRADE.md. Only .form-label needed a shim
(forms.scss). Browser-verified home carousel+navbar, signup form + terms
checkbox, login form; REST smoke byte-identical.

imports/ui/components/NavItem/NavItem.js

@@ -2,9 +2,9 @@ import classNames from 'classnames';
 import React from 'react';
 import PropTypes from 'prop-types';
 
-import { SafeAnchor } from 'react-bootstrap';
-import createChainedFunction from 'react-bootstrap/lib/utils/createChainedFunction';
-
+// Self-contained NavItem. The old one wrapped react-bootstrap 0.31's
+// `SafeAnchor` + `createChainedFunction` (both gone in v2); the markup this
+// navbar needs is just an <li><a> that toggles the collapsed menu on click.
 const propTypes = {
   active: PropTypes.bool,
   disabled: PropTypes.bool,
@@ -12,7 +12,11 @@ const propTypes = {
   href: PropTypes.string,
   onClick: PropTypes.func,
   onSelect: PropTypes.func,
-  eventKey: PropTypes.any
+  eventKey: PropTypes.any,
+  className: PropTypes.string,
+  anchorClassName: PropTypes.string,
+  style: PropTypes.object,
+  children: PropTypes.node
 };
 
 const defaultProps = {
@@ -21,42 +25,35 @@ const defaultProps = {
 };
 
 class NavItem extends React.Component {
-  constructor(props, context) {
-    super(props, context);
-
+  constructor(props) {
+    super(props);
     this.handleClick = this.handleClick.bind(this);
   }
 
   handleClick(e) {
-    if (this.props.onSelect) {
+    const { disabled, onClick, onSelect, eventKey } = this.props;
+    if (disabled) {
       e.preventDefault();
-
-      if (!this.props.disabled) {
-        this.props.onSelect(this.props.eventKey, e);
-      }
+      return;
+    }
+    if (onClick) onClick(e);
+    if (onSelect) {
+      e.preventDefault();
+      onSelect(eventKey, e);
     }
   }
 
   render() {
     const {
-      active, disabled, onClick, className, anchorClassName, style, ...props
-    } =
-      this.props;
+      active, disabled, role, href, onClick, onSelect, eventKey,
+      className, anchorClassName, style, children, ...props
+    } = this.props;
 
-    delete props.onSelect;
-    delete props.eventKey;
+    const anchorProps = { ...props };
+    if (href) anchorProps.href = href;
+    anchorProps.role = role || (href === '#' ? 'button' : undefined);
+    if (role === 'tab') anchorProps['aria-selected'] = active;
 
-    // These are injected down by `<Nav>` for building `<SubNav>`s.
-    delete props.activeKey;
-    delete props.activeHref;
-
-    if (!props.role) {
-      if (props.href === '#') {
-        props.role = 'button';
-      }
-    } else if (props.role === 'tab') {
-      props['aria-selected'] = active;
-    }
     return (
       <li
         role="presentation"
@@ -65,12 +62,14 @@ class NavItem extends React.Component {
         className={classNames(className, { active, disabled })}
         style={style}
       >
-        <SafeAnchor
-          {...props}
-          disabled={disabled}
+        {/* eslint-disable-next-line jsx-a11y/anchor-is-valid */}
+        <a
+          {...anchorProps}
           className={anchorClassName}
-          onClick={createChainedFunction(onClick, this.handleClick)}
-        />
+          onClick={this.handleClick}
+        >
+          {children}
+        </a>
       </li>
     );
   }