Add optional send message pushbutton on web ui (chatbox component)

src/main/resources/configuration.txt

@@ -90,6 +90,8 @@ components:
     messagettl: 5
     # Optional: set number of lines in scrollable message history: if set, messagettl is not used to age out messages
     #scrollback: 100
+    # Optional: send push button
+    sendbutton: false
   - class: org.dynmap.ClientComponent
     type: playermarkers
     showplayerfaces: true