Feature/refactor to feature first

This MR has two objectives:

• Refactor the main folder tree structure to follow the pattern Feature First
• Separate the logic and view for some critical screens (for example post_details screen or publish screen)

Benefits:

• More structured code, easily scalable
• Easier to extract the existing logic code from the view into services/providers/controllers
• Easier to create tests and mock classes
• Easier to detect code regressions