Implement login page

http://54.254.139.254/kunagi/#project=300222bf-836d-437a-b2cd-ea21f3adc38a-1%7Cpage=Whiteboard%7Centity=5fa6b9e2-ffd7-46a1-85d0-5c11f221580e-1

To implement this, the header code and footer code is copied from
index.html, and used semantic-ui Lib directly.
Also added and link to login page in index page.

The 'sign on' UI is not implemented, will do that later if needed.