more admin dashboard polish, some code cleanup

admin/static/tracks.js

@@ -0,0 +1,24 @@
+const newTrackBtn = document.getElementById("create-track");
+if (newTrackBtn) newTrackBtn.addEventListener("click", event => {
+    event.preventDefault();
+    const title = prompt("Enter an title for this track:");
+    if (title == null || title == "") return;
+
+    fetch("/api/v1/track", {
+        method: "POST",
+        headers: { "Content-Type": "application/json" },
+        body: JSON.stringify({title})
+    }).then(res => {
+        res.text().then(text => {
+            if (res.ok) {
+                location = "/admin/tracks/" + text;
+            } else {
+                alert(text);
+                console.error(text);
+            }
+        })
+    }).catch(err => {
+        alert("Failed to create track. Check the console for details.");
+        console.error(err);
+    });
+});