US49Como usuario quiero ver la funcionalidad completa de la activity "Onboarding 2" para poder continuar con el tour, volver atrás o saltar el tour

[todotirreno]

• Add content description for image in Onboarding2
• Add @string attributes in activity_onboarding2.xml
• Update colors in activity_onboarding2.xml according to accesibility guidelines
• Change font size to sp in activity_onboarding2.xml

closes #107