Started working on the frontend

- Added the new post frontend
- Hooked up publishing of posts to the site publisher
- Added an site exporter as a publishing target

assets/css/main.css

@@ -0,0 +1,15 @@
+@import "bootstrap/dist/css/bootstrap.css";
+
+.post-form {
+    display: grid;
+    grid-template-rows: min-content auto min-content;
+    position: absolute;
+    top: 0;
+    bottom: 0;
+    left: 0;
+    right: 0;
+}
+
+.post-form textarea {
+    height: 100%;
+}