Minor fixes for studydocs

An standardized error 401 page was added.

Search for studydocs was made case insensitive.

src/views/errors.js

+const m = require('mithril');
+
+export class Error401 {
+  static view() {
+    return m('div', 'This page is only accessible for authenticated users. Please log in.');
+  }
+}
+
+export class Error404 {
+  static view() {
+    return m('div', 'This page does not exist.');
+  }
+}