Resolve "Add "about" page"

Closes #81

See merge request !77

Resolve "Add "settings" page"

Closes #79

See merge request !74

Resolve "Restore "save / resume game" feature"

Closes #80

See merge request !76

Resolve "Add "settings / game / board / cell" models"

Closes #74

See merge request !73

Resolve "Add a delay after use help button to reactivate"

Closes #43

See merge request !45

Resolve "Improve game architecture"

Closes #73

See merge request !68

Merge branch '78-improve-ci-cd-remove-update-step-disable-build-debug-in-master-branch' into 'master'

Resolve "Improve CI/CD, remove "update" step, disable "build-debug" in master branch"

Closes #78

See merge request !72

Resolve "Avoid print calls in production code"

Closes #77

See merge request !71

Resolve "Remove deprecation in flutter gradle plugin"

Closes #76

See merge request !70

Resolve "Use flutter linter and apply lints"

Closes #75

See merge request !69

Resolve "Upgrade framework, build tools and dependencies"

Closes #72

See merge request !67

Resolve "Remove iOS variant"

Closes #70

See merge request !66

Resolve "Upgrade flutter framework and dependencies"

Closes #71

See merge request !65

Resolve "Enable splash screen"

Closes #69

See merge request !64

Resolve "Save current game, allow resume / restart"

Closes #51

See merge request !62

Resolve "Upgrade flutter framework and dependencies, clean/update code"

Closes #68

See merge request !63

Resolve "Improve app metadata, include fdroid metadata in repository"

Closes #67

See merge request !61

Resolve "Upgrade flutter framework and dependencies"

Closes #66

See merge request !60

Resolve "Add/improve levels"

Closes #64

See merge request !58

Resolve "Fix back to menu button"

Closes #62

See merge request !56