Added Feature Auto Clipboard Sync

[0xAungkon]

Added Feature Auto Clipboard Sync Though Html Dom Event & navigator.clipboard

Note: Clipboard only serves over https . so do following tasks :

1. Create a pem file openssl req -x509 -newkey rsa:2048 -keyout self.pem -out self.pem -days 365 -nodes
2. Make sure to add --ssl-only in the end of command ./utils/novnc_proxy --vnc localhost:5901--ssl-only

Holla clipboard sync automatically like charm . No mouse copy paste.

[0xAungkon]

@jswanner @nbibler @thekvn @retr0h please review the pull request .

[xy3xy3]

Failed to read from clipboard: NotAllowedError: Failed to execute 'readText' on 'Clipboard': Document is not focused.
at HTMLDocument. (vnc.html:349:56)

[liyimeng]

what is the PR trying to achieve?
I deploy it. Expecting I can do copy on my local machine and paste it into the remote machine which I connect via vnc, but nothing happen.