Refactor and simplify Item Getting Guide item list CSS a bit

Notably, we're renaming `.add-to-cart-cell` to `.actions-cell`, in
preparation for other potential actions in other categories!

app/assets/stylesheets/items/sources.sass

@@ -17,15 +17,15 @@
 		&:last-child
 			padding-right: .5em
 
-	.thumbnail-cell
-		img
+	.thumbnail-cell img
 		display: block
 		width: 2.5em
 		height: 2.5em
 
-	.add-to-cart-cell
+	.actions-cell
 		text-align: right
 		padding-left: 1em
+		font-size: 85%
 
 	thead
 		background: $module-bg-color
@@ -33,9 +33,6 @@
 		th
 			text-align: left
 
-		.add-to-cart
+		.actions-cell button
 			/* Bootstrap's Purple 600 */
 			+awesome-button-color(#59359a)
-
-	.add-to-cart
-		font-size: 85%

app/views/items/sources.html.haml

@@ -18,16 +18,16 @@
 					Total: #{@nc_mall_items.map(&:current_nc_price).sum} NC
 					(#{pluralize @nc_mall_items.size, "item"})
 						
-					%td.add-to-cart-cell
-						%button.add-to-cart{onclick: "alert('Todo!')"}
+					%td.actions-cell
+						%button{onclick: "alert('Todo!')"}
 							Buy all in NC Mall
 		%tbody
 			- @nc_mall_items.each do |item|
 				%tr
 					%td.thumbnail-cell= item_thumbnail_for(item)
 					%td= item.name
-					%td.add-to-cart-cell
-						%button.add-to-cart{onclick: "alert('Todo!')"}
+					%td.actions-cell
+						%button{onclick: "alert('Todo!')"}
 							Buy (#{item.current_nc_price} NC)
 
 - if @np_items.present?