REV: make Room class in a standalone module file
REV: refactor socket/index.js
REV: clean sockets/index.js

Change-Id: Id4286e78dc2bd972acea00271182fa3810f42f7f
REV: fix typo
REV: fix another same typo
REV: change placeholder of username input in login page

Placeholder `Username` is more general than `Kerberos name` due to we cannot
assume what authentication is used.
Merge pull request #2 from tkdchen/master

make Room class in a standalone module file