Create manager that allow to work with files

[EvilLord666]

We should create controller that allow us to store small files in server FS

[stdstring]

Why only for small files? And which size is small for this case?

[EvilLord666]

@stdstring because it is a simplified common solution, small means that it have size less then 50Mb.

[EvilLord666]

This task is partially done, what should we do additionally (TODO list)
* [ ] Add controller for Files manipulation (FileController)

• Docs in method
• Optimize messaging (move some in ResponseMessageBuilder i.e. for Conflict statuses)
• Implement Update method
• Write tests

Additionally (should decide whether we need it or not):
* [ ] Add GRPC analog of FileController

[EvilLord666]

It seems that WebApiToolkit just should have only FileManager during this issue implementation

[EvilLord666]

Done, manager was created