Update packages & major refactoring of widgets and files

[GAM3RG33K]

• update code to comply with new norms in flutter 2.0
• enforce code standards by using pedantic package
• separate a collection widgets & widget utility methods in their own files
• add & improve code comments
• update example code, use new functions or features for demo and use color pick event to update app's accent color on the go

Signed-off-by: Harshvardhan Joshi hj2931996@gmail.com