Migrate Jade to Pug template engine

Jade templates engine has been renamed to Pug.

We are using Pug already on the Blender Cloud repository, following is Flamenco and Attract

src/templates/errors/403_embed.pug

@@ -1,4 +1,4 @@
-#error-container(class="error-403")
+#error-container.error-403
 	#error-box
 		.error-top-container
 			.error-title Forbidden.

src/templates/errors/404_embed.pug

@@ -1,4 +1,4 @@
-#error-container(class="error-404")
+#error-container.error-404
 	#error-box
 		.error-top-container
 			.error-title Not found.

src/templates/errors/412.pug

@@ -1,6 +1,6 @@
 | {% extends "errors/layout.html" %}
 | {% block body %}
-#error_container.412.standalone
+#error_container.error-412.standalone
 	#error_box
 		.error-title 412. Precondition Failed.
 

src/templates/errors/412_embed.pug

@@ -1,4 +1,4 @@
-#error_container.412
+#error_container.error-412
 	#error_box
 		.error-title 412. Precondition Failed.
 

src/templates/errors/500.pug

@@ -21,7 +21,7 @@ html(lang="en")
 
 	body.error
 
-		#error_container.500.standalone
+		#error_container.error-500.standalone
 			#error_box
 				.error-top-container
 					.error-title Something went wrong.

src/templates/errors/500_embed.pug

@@ -1,4 +1,4 @@
-#error_container.500
+#error_container.error-500
 	#error_box
 		.error-top-container
 			.error-title Something went wrong.

src/templates/users/edit_embed.pug

@@ -89,7 +89,7 @@ script(type="text/javascript").
 		//- console.log($(this).serialize());
 		$.post($(this).attr('action'), $(this).serialize())
 		.done(function(data){
-			// This function is defined in index.jade.
+			// This function is defined in index.pug.
 			displayUser('{{ user._id }}')
 			.done(function() {
 				$('#user-edit-notification').addClass('success').html('Success!');

src/templates/users/index.pug

@@ -103,7 +103,7 @@ script(src="{{ url_for('static_pillar', filename='assets/js/vendor/jquery.select
 
 script(type="text/javascript").
 
-	// This function is also used in edit_embed.jade.
+	// This function is also used in edit_embed.pug.
 	function displayUser(userId) {
 		var url = '/u/' + userId + '/edit';
 		return $.get(url, function(dataHtml){