Bass acadamy onboarding page tweaks

Did some minor improvements to the flow and visual tweaks to the onboarding process of my side project Bass Acadamy.

- Fixed the style of the buttons of the plans to focus on the pro plan with only one primary button
- Switched the ordering of the flow so the user selects if they're a student or teacher first
- Re-did the onboarding pages as modals than new pages for a better inline experience