Refactored by implementing the widget: 'bottom_sheet' and changing the...

Refactor: ‘-bottom-up-sheet’ reusable-widget and its usage all over the app.

Refactored by implementing the widget: 'bottom_sheet' and changing the structure of child widgets. Changed order of the methods/widgets. Applyied lint suggestions. Added/updated coments. Corrected white-spacings/line-breakings.