"writeImage" method support for windows

[alexkmbk]

Two dependences were added: import 'package:path/path.dart' as Path; import 'package:uuid/uuid.dart';

And also the warning level was decreased to /W3 in CMakeLists.txt file.

So I am not sure if it is appropriate changes for this project, it is up to the maintainer to decide.

[alexkmbk]

https://github.com/MixinNetwork/flutter-plugins/issues/131

[narumi147]

@boyan01 is there anything block this pr to be merged? It seems works fine on windows

[boyan01]

Sorry for the delay. Thanks for the PR!