Fix class names in some more places.

Related to the PSR-4 move via 865ecc8796

js/Article.js

@@ -352,7 +352,7 @@ const Article = {
 			title: __("Article tags"),
 			content: `
 				${App.FormFields.hidden_tag("id", id.toString())}
-				${App.FormFields.hidden_tag("op", "article")}
+				${App.FormFields.hidden_tag("op", "Article")}
 				${App.FormFields.hidden_tag("method", "setArticleTags")}
 
 				<header class='horizontal'>

js/CommonDialogs.js

@@ -35,7 +35,7 @@ const	CommonDialogs = {
 							content: `
 								<form onsubmit='return false'>
 
-									${App.FormFields.hidden_tag("op", "feeds")}
+									${App.FormFields.hidden_tag("op", "Feeds")}
 									${App.FormFields.hidden_tag("method", "add")}
 
 									<div id='fadd_error_message' style='display : none' class='alert alert-danger'></div>

js/PrefHelpers.js

@@ -280,7 +280,7 @@ const	Helpers = {
 						${__("You can override colors, fonts and layout of your currently selected theme with custom CSS declarations here.")}
 					</div>
 
-					${App.FormFields.hidden_tag('op', 'rpc')}
+					${App.FormFields.hidden_tag('op', 'RPC')}
 					${App.FormFields.hidden_tag('method', 'setpref')}
 					${App.FormFields.hidden_tag('key', 'USER_STYLESHEET')}