Resolve "Upgrade framework and dependencies"

Closes #99

See merge request !95

Resolve "Upgrade Android Gradle Plugin"

Closes #98

See merge request !94

Resolve "Use private repository for package flutter_custom_toolbox"

Closes #97

See merge request !93

Resolve "Update dependencies, improve/fix some UI/UX"

Closes #96

See merge request !92

Resolve "Upgrade framework and dependencies"

Closes #95

See merge request !91

Resolve "Use navigation widgets from flutter_custom_toolbox"

Closes #94

See merge request !90

Resolve "Use ActivityParameters widgets from flutter_custom_toolbox"

Closes #93

See merge request !89

Resolve "Use activity buttons widgets from flutter_custom_toolbox"

Closes #91

See merge request !88

Resolve "Restore custom font"

Closes #92

See merge request !87

Resolve "Normalize Activity application architecture"

Closes #90

See merge request !86

Resolve "Use ApplicationSettings widgets from flutter_custom_toolbox"

Closes #89

See merge request !85

Resolve "Use flutter_custom_toolbox for common features"

Closes #88

See merge request !84

Resolve "Re-order ABI builds"

Closes #87

See merge request !83

Resolve "Improve build process"

Closes #86

See merge request !82

Resolve "Clean / improve / update code"

Closes #85

See merge request !81

Resolve "Normalize game architecture"

Closes #83

See merge request !79

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