Added script to make list of headers

Added a new script with the purpose of getting all headers from a post's content and creating links for them in the left sidebar.
Some div classes have been modified, and a wrapper div has been added to posts because of this new script.
Some minor CSS changes have been made.

assets/js/get-headers-list.js

@@ -0,0 +1,16 @@
+$(document).ready(function () {
+    const headers = $(".mind-post_content h2, .mind-post_content h3").toArray();
+    const sidebar = $("#mind-post_sidebar-left");
+
+    for (let i = 0; i < headers.length; i++) {
+        const currentHeader = headers[i];
+        const headerText = $(currentHeader).text();
+        const headerId = $(currentHeader).attr("id");
+        const headerType = $(currentHeader).prop("nodeName").toLowerCase();
+
+        // <h2> <a href="header-linke"> Header Name </a> </h2>
+        const newLine = "<" + headerType + "> <a href=\"#" + headerId + "\">" + headerText + "</a> </" + headerType + ">";
+        sidebar.append(newLine);
+    }
+});
+