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/homebrew/brewRenderer/toolBar/toolBar.less

@@ -34,6 +34,13 @@
 		align-items : center;
 	}
 
+	.anchored-box {
+		color: #CCCCCC;
+		input[type='number']{
+			width: 4ch;
+		}
+	}
+
 	input {
 		position       : relative;
 		height         : 1.5em;