Null safety (+ remove redundant example subdirectory)

[sjmallon]

Simplest changes to achieve null safety, including dependency upgrades and deletion of the example subdirectory, which was just the standard outdated flutter example and would have needed pointless changes.

[hamza72x]

Thanks

Using like -

dev_dependencies:
  flutter_native_splash: ^1.0.3
  flutter_launcher_icons: ^0.9.0
  flutter_launcher_name:
    git:
      url: https://github.com/sjmallon/flutter_launcher_name
      ref: adcd03ac5ee7609d4e9c61c9d6b246a7a083dcf4