Add button to toggle Preview tools

Toggles a state variable to either visible or hidden which is used to set a related class on the toolbar.  The hiding is done with CSS, just reducing the width of the toolbar and the opacity of the tools.

client/homebrew/brewRenderer/toolBar/toolBar.jsx

@@ -11,6 +11,7 @@ const ToolBar = ({ onZoomChange, currentPage, onPageChange, totalPages })=>{
 
 	const [zoomLevel, setZoomLevel] = useState(100);
 	const [pageNum, setPageNum]     = useState(currentPage);
+	const [toolsVisible, setToolsVisible] = useState(true);
 
 	useEffect(()=>{
 		onZoomChange(zoomLevel);
@@ -66,8 +67,9 @@ const ToolBar = ({ onZoomChange, currentPage, onPageChange, totalPages })=>{
 		return deltaZoom;
 	};
 
-	return (
-		<div className='toolBar'>
+	return (		
+		<div className={`toolBar ${toolsVisible ? 'visible' : 'hidden'}`}>
+			<button class='toggleButton' title={`${toolsVisible ? 'Hide' : 'Show'} Preview Toolbar`} onClick={()=>{setToolsVisible(!toolsVisible)}}><i className='fas fa-glasses' /></button>
 			{/*v=====----------------------< Zoom Controls >---------------------=====v*/}
 			<div className='group'>
 				<button

client/homebrew/brewRenderer/toolBar/toolBar.less

@@ -15,6 +15,10 @@
 	font-family      : 'Open Sans', sans-serif;
 	color            : #CCCCCC;
 	background-color : #555555;
+	& > *:not(.toggleButton) {
+		opacity: 1;
+		transition: all .2s ease;
+	}
 
 	.group {
 		box-sizing       : border-box;
@@ -100,4 +104,25 @@
 			font-size:1.2em;
 		}
 	}
+
+	&.hidden {
+		width: 32px;
+		transition: all .3s ease;
+		flex-wrap:nowrap;
+		overflow: hidden;
+		background-color: unset;
+		opacity: .5;
+		& > *:not(.toggleButton) {
+			opacity: 0;
+			transition: all .2s ease;
+		}
+	}
+}
+
+button.toggleButton {
+	z-index : 5;
+	position:absolute;
+	left: 0;
+	width: 32px;
+	min-width: unset;
 }