feat: loads of improvements (see comments)

1) check whether submitting user is submitting for himself
2) some refactoring of the tabs in `Ranking`
3) get chemistry and mvps from DB
4) restore previous
5) start over
6) (hopefully) improve logout

src/App.css

@@ -235,15 +235,17 @@ h3 {
   margin: auto;
 }
 
-button,
-.button {
+button {
   margin: 4px;
   font-weight: bold;
-  font-size: large;
   color: aliceblue;
   background-color: black;
   border-radius: 1.2em;
   z-index: 1;
+
+  &:hover {
+    opacity: 75%;
+  }
 }
 
 #control-panel {