Use jumbo emoji for short emoji-only messages (#207)

* Display messages containing only <7 emoji bigger

* Amending PR: Address mentioned concerns

This fixes several concerns raised during the PR review process.  A summary of the changes
implemented is below:
- Size jumbo emoji using the text-h1 class, instead of hardcoding a size
- Increase the emoji limit to 10
- Re-wrap m.text messages in a p tag, fixing a bug where newlines were lost

src/app/molecules/message/Message.scss

@@ -198,6 +198,7 @@
       opacity: 0;
     }
   }
+
   .data-mx-spoiler--visible {
     background-color: var(--bg-surface-active) !important;
     color: inherit !important;