Reorganize all the code to be modular and clean

[sungchun12]

• Make it really easy to follow code logic and entry and exit points
• Bias towards one way data flow given streamlit reads the code top to bottom and most of the logic follows a linear path: https://dev.to/laserreindeer/one-way-data-flow-why-47fk
• State travels from parent to child classes/objects