Shrink some styles

Group update font and sender names should be smaller.

stylesheets/manifest.css

@@ -128,6 +128,13 @@ body, input {
 body {
   margin: 0; }
 
+.group-update {
+  font-size: smaller; }
+
+.sender {
+  font-size: smaller;
+  opacity: 0.8; }
+
 .title-bar {
   position: fixed;
   top: 0;

stylesheets/view/_conversation.scss

@@ -11,6 +11,15 @@ body {
   margin: 0;
 }
 
+.group-update {
+  font-size: smaller;
+}
+
+.sender {
+  font-size: smaller;
+  opacity: 0.8;
+}
+
 .title-bar {
   position: fixed;
   top: 0;