added logos, style and some adjustments

app/__init__.py

app/models.py

app/routes.py

app/static/css/slider.css

app/static/img/onni_LOGO-RGB-transparent_bg.png

app/static/img/onni_LOGO-RGB-transparent_bg_cut.png

app/static/img/onni_LOGO-horizontal-RGB-transparent_bg.png

...tatic/img/onni_LOGO-horizontal-RGB-transparent_bg_cut.png

...tatic/img/onni_LOGO-horizontal-RGB-transparent_bg_cut.xcf

app/templates/base.html

app/templates/consent.html

app/templates/index.html

app/templates/instructions.html

app/templates/view_experiment.html

app/translations/el/LC_MESSAGES/messages.mo

app/translations/el/LC_MESSAGES/messages.po

app/translations/en/LC_MESSAGES/messages.mo

app/translations/en/LC_MESSAGES/messages.po

app/translations/fa/LC_MESSAGES/messages.mo

app/translations/fa/LC_MESSAGES/messages.po