Use inherited font-family on the message input

Chrome's UA stylesheet defaults font-family to monospace on textareas.

The only other textarea at the moment is the debug log, where monospace
is actually nice to have since it's more scannable.

// FREEBIE

stylesheets/_conversation.scss

@@ -560,6 +560,7 @@
     z-index: 5;
     resize: none;
     font-size: 1em;
+    font-family: inherit;
   }
 }
 

stylesheets/manifest.css

@@ -994,7 +994,8 @@ input.search {
     outline: 0;
     z-index: 5;
     resize: none;
-    font-size: 1em; }
+    font-size: 1em;
+    font-family: inherit; }
 
 .toast {
   position: absolute;