Added background sync support

This release adds background sync with the ability to set a custom interval in the settings.

BUGFIX new logo, proper login error and new target api

• use new logo as launcher logo
• on login error, the app now gives only one error
• updated notification logo to be centered

Added error handling with proper notifications, added update notifications, fixed some bugs

• Every time a request fails the user will now get a proper error message
• App checks for updates on startup and notifies the user. this can be turned off in the settings
• setting 'repeat after' should now work

BUGFIX: Namespace list does not load after adding a favourite or sharing a list

This release fixes issue #21 by making the owner field of a namespace nullable.

v0.0.21-alpha

What's Changed

• migration to null safety. Improves performance dramatically.
• Bugfixes in edit task page.
• null-safety & some other cleanup by @k9withabone in #16
• Null safety fixes by @k9withabone in #17

Many thanks to @k9withabone for his dedication to this project!

Full Changelog: v0.0.20-alpha...v0.0.21-alpha

Switched back to package:http for stability

Changelog

• switched back to package:http library for stability
• fixed certificate ignoring. (be advised: sometimes the app needs to be restarted for settings to take effect)
• fixed bug where list was saved to namespace with id = 0 when editing
• fixed 'Expected type after 'as'' by @Szymek887 in #14

Kanban view & OTP fix & self-signed certs

This release adds:

• kanban view to lists (many thanks to @k9withabone)
• support for self-signed certificates

And fixes:

• login via one time passcodes

BUGFIX fixed typeahead and adding labels

fixed old method call for getting labels

fixed wrong datetime stamp for labels

BUGFIX displaying lists without done tasks fixed

v0.0.17-alpha

removed unnecessary statement

BUGFIX no items when list is shorter than maxpagelength

Bugfixes

• Some list items are not loaded when list is too short
• App freezes when button 'login via webview' is pressed without entering anything