fix: list item formatting for lists with paragraphs (#1283)

This removes the fancy tick-mark next to unordered list items, which is
a little depressing, but fixes formatting for them when they contain
paragraphs (`<p>` elements). The tick-mark has been replaced with
a square mark. Both ordered and unordered lists have grown 1rem of left
padding to compensate for their position.

Considered using disclosure-closed as a similar triangle replacement,
but it's not regarded as something that should be used in production
(per MDN). Using a simple string is unsupported because it's only in
a CSS working draft, so a square is the least controversial option,
I think.

Closes #1282.

client/themes/default/scss/app.scss

@@ -312,8 +312,8 @@
   // ---------------------------------
 
   ol, ul {
-    padding: 1rem 0 0 0;
+    padding: 1rem 0 0 1rem;
-    list-style-position: inside;
+    list-style-position: outside;
 
     li > ul, li > ol {
       padding-top: .5rem;
@@ -435,14 +435,7 @@
   }
 
   ul {
-    list-style: none;
+    list-style: square outside;
-
-    > li::before {
-      content: '\25b8';
-      color: mc('grey', '600');
-      display: inline-block;
-      width: 1.35rem;
-    }
   }
 
   // ---------------------------------