responsive frontpage implemented

..._tuw/assets/semantic-ui/less/invenio_theme_tuw/theme.less

...io_theme_tuw/static/images/planned-features/analytics.png

...o_theme_tuw/static/images/planned-features/connection.png

invenio_theme_tuw/static/images/planned-features/group.png

invenio_theme_tuw/static/images/planned-features/user.png

invenio_theme_tuw/static/images/planned-features/version.png

...e_tuw/templates/semantic-ui/invenio_theme_tuw/footer.html

...uw/templates/semantic-ui/invenio_theme_tuw/frontpage.html

...e_tuw/templates/semantic-ui/invenio_theme_tuw/header.html