Third Beta - Improvements and Fixes

Description:

The third beta adds a lot of useful changes and fixes a lot of smaller issues.

Changelog:

• A substantial code refractor of the user interface to cleanup code and remove use of global variables.
• Added an option to change the username in the settings.
• Improve the experience on the first start of the application.
• Better password input checking when changing it inside the settings.
• Switch from AES-256 to AES-512/256 (breaking change).
• Avoid code duplication between share and file operation code.
• Major sort change to sort all exercises after when they occurred instead of when they were added.
• Fix an issue where nothing would be displayed if the exercises file existed but still was empty after several app starts.
• Make sure that the settings reset to light theme and not dark (missed during change of default).
• Switch between login entry widgets using key up and key down.
• Abort and show error if user tries to share with nothing to share.
• Use the correct way to change selected option in the theme switcher.