Added toggle for download messages/paste images additions

When room is locked there is no UI to indicate that you cannot download
messages #1055

* Added new download icons
* Added toggleDownloadButton to Chat.ui.js
* Updated room methods to change button status on room change and lock
  change
* Updated paste dialog with new keyhandlers for <esc> and <enter>
* Focus message box after dialog closed.


![](https://jabbrlive.blob.core.windows.net/jabbr-uploads/clipboard_8b05.png)