replaced nuovo-rilascio.html with latest-version.html

added new static page (Edubuntu, Ubuntu Cinnamon and Ubuntu Unity)
with relative imgs

now build_scss takes all .scss files contained inside assets and build and minify them with min.css extension

Fixes: issue #31

now info.json has 'long_description' and 'portrait' key with img or video path

Fixes: issue #28

by using the 'releases' key in constants.json

Fixes: issue #27

added static/assets folder in gitignore