Feature/284 nothing here yet labels (#393)

* Add not yet label for file upload

* Fix wrong heading on course dashboard

Author: Jasperhino

app/views/courses/show.html.erb

@@ -16,7 +16,7 @@
 <br>
 
 <section>
-  <h2>Files</h2>
+  <h2>Materials</h2>
   <div class="d-flex justify-content-between nav-tabs">
     <ul class="nav w-100" id="fileTabs" role="tablist">
       <li class="nav-item">