Chat input scrollback/history with additional fixes

Added input scrollback via up and down arrow keys - Closes #121 
Escape key clears the message input box
Combining sendMessage code between pressing enter and clicking send
Let the onchange event of #chat-input enable/disable the send button
Only send a message if there is a message to send.
    Previously, you could click the send button with an empty
    message input, and a blank line would appear in the chat window.