Teleport v1.3 Relase

This release includes several major new features and it's recommended for production use.

New Features:

• Support for hardware U2F keys for 2nd factor authentication.
• CLI client profiles: tsh can now remember its --proxy setting.
• tctl auth sign command to allow administrators to generate user session keys
• Web UI is now served directly from the executable (no more need for web assets in /usr/local/share/teleport)

Bug Fixes:

• Multiple auth servers in config doesn't work if the last on is not reachable. #593
• tsh scp -r does not handle directory upload properly #606