add support for setting points, tokens, and broadcasting control msgs

Control messages are messages that are broadcast to all clients and have
no clearly defined content.  The idea is that this can be used to
control a monitor without having to keep adding support for specific
commands on the protocol layer.
This also changes some of the existing messages and adds another
ridiculous convenience layer to our HTML/JS templating: data-eval.
We should probably just bite the bullet and use some reactive framework.

public/buzzer.css

@@ -2,6 +2,13 @@ body {
   font-family: sans-serif;
   overflow: hidden;
 }
+body.admin #info {
+  position: unset;
+}
+body.player .admin-only,
+body.admin .player-only {
+  display: none !important;
+}
 #error {
   background-color: #fee;
   border: 3px solid red;
@@ -9,6 +16,9 @@ body {
   font-family: monospace;
   display: none;
 }
+body.error #error {
+  display: block;
+}
 #error code {
   white-space: pre;
 }
@@ -51,6 +61,9 @@ ul {
 .player.buzzing.too-late::before {
   content: "🥈 ";
 }
+.player div.admin-only {
+  display: inline-block;
+}
 #info {
   position: absolute;
 }
@@ -60,7 +73,6 @@ ul {
   align-items: center;
   width: 100%;
   height: 90%;
-  /*position: absolute;*/
 }
 #active {
   color: red;