Add 'nodejs' role

nodejs role installs NodeJS (server-side JavaScript application
platform) from Debian Backports and npm (nodejs package manager) using
official installation script (will be changed to .deb package if it
becomes available in Debian Backports).
Add option to disable favicon filtering in nginx

By default nginx server template filters out requests for favicon.ico,
so that they do not appear in the access logs. Becauce of that, if
favicon.ico is served to the user by different means (for example,
application server itself), request is not passed through. Adding
'favicon: False' to server configuration options will disable this
functionality and allow serving of favicon.ico as normal.
Add 'etherpad' role

Etherpad (Lite) is a collaborative web text editor written in NodeJS.
This role will install Etherpad behind nginx reverse proxy, on it's own
subdomain (pad.{{ ansible_domain }}).

By default it is publicly accessible, 'admin' account is automatically
created and configured if 'secret' role is enabled. Default database
used by Etherpad is MySQL, other databases will be added in the future.
Merge pull request #67 from drybjed/role/etherpad

Added Etherpad role with required dependencies