Add View Mode Options

Adds a new AnchoredBox component that is functionally a clone of the "saving error" notifications, but drops a lot of the JS in favor of the new (chrome-only!) CSS Anchor Positioning API.  In subsequent commits, either alternate styling or a polyfill will be added non-supported browsers.

The box contains a few inputs that modify the CSS applied to `.pages`, most critically a "start on right" toggle for the Facing Pages mode.

client/components/anchoredBox.jsx

@@ -0,0 +1,55 @@
+require('./anchoredBox.less');
+import React, { useState, useRef, useEffect } from 'react';
+
+const AnchoredBox = ({ anchorPoint = 'center', className, children, ...props })=>{
+	const [visible, setVisible] = useState(false);
+	const triggerRef = useRef(null);
+	const boxRef = useRef(null);
+
+	useEffect(()=>{
+		const handleClickOutside = (evt)=>{
+			if(boxRef.current &&
+				!boxRef.current.contains(evt.target) &&
+				triggerRef.current &&
+				!triggerRef.current.contains(evt.target)){
+				setVisible(false);
+			}
+		};
+		window.addEventListener('click', handleClickOutside);
+
+		const iframe = document.querySelector('iframe');
+		if(iframe) {
+			iframe.addEventListener('load', ()=>{
+				const iframeDoc = iframe.contentWindow.document;
+				if(iframeDoc) {
+					iframeDoc.addEventListener('click', handleClickOutside);
+				}
+			});
+		}
+
+		return ()=>{
+			window.removeEventListener('click', handleClickOutside);
+			if(iframe?.contentWindow?.document) {
+				iframe.contentWindow.document.removeEventListener('click', handleClickOutside);
+			}
+		};
+	}, []); // Empty dependency array to run effect on mount only
+
+	const handleClick = ()=>{
+		setVisible(!visible);
+	};
+
+	return (
+		<>
+			<button className={`${className} anchored-trigger${visible ? ' active' : ''}`} onClick={handleClick} ref={triggerRef}>
+				<i className='fas fa-gear' />
+			</button>
+			<div className={`anchored-box${visible ? ' active' : ''}`}  ref={boxRef}>
+				<h1>{props.title}</h1>
+				{children}
+			</div>
+		</>
+	);
+};
+
+export default AnchoredBox;