Enable doc section expand/collapse

Closes #170

gui/app/styles/core/icon-ui.scss

@@ -438,3 +438,11 @@ icons
 .dicon-move-layer-up::before {
   content: "\ea5d";
 }
+
+.dicon-alpha-order::before {
+  content: "\ea5e";
+}
+
+.dicon-enlarge::before {
+  content: "\ea5f";
+}

gui/app/styles/core/layout/sidebar.scss

@@ -20,6 +20,21 @@
 		}
 	}
 
+	// Allows for icon to be placed top right corner of sidebar zone.
+	// Expects icon to be placed in the zone.
+	> .custom-action {
+		position: absolute;
+		top: 10px;
+		right: 10px;
+		cursor: pointer;
+		color: map-get($gray-shades, 500);
+		font-size: 1rem;
+
+		&:hover {
+			color: map-get($gray-shades, 800);
+		}
+	}
+
 	> .section {
 		margin: 0;
 		padding: 0 7px;

gui/app/styles/core/view/document/section.scss

@@ -55,6 +55,14 @@
 				color: map-get($yellow-shades, 700);
 			}
 		}
+
+		> i.expand {
+			color: map-get($green-shades, 500);
+
+			&:hover {
+				color: map-get($green-shades, 700);
+			}
+		}
 	}
 }