Consider reorganizing folder structure to follow current conventions

[nanotaboada]

• Organizing and testing projects with the .NET CLI
  https://learn.microsoft.com/en-us/dotnet/core/tutorials/testing-with-cli

/Dotnet.Samples.AspNetCore.WebApi

|__/src
  |__/Dotnet.Samples.AspNetCore.WebApi
      |__Dotnet.Samples.AspNetCore.WebApi.csproj
      |__/Controllers
      |__/Data
      |__/Migrations
      |__/Models
      |__/Services
      |__Program.cs

|__/tests
  |__/Dotnet.Samples.AspNetCore.WebApi.Tests
      |__Dotnet.Samples.AspNetCore.WebApi.Tests.csproj

Dotnet.Samples.AspNetCore.WebApi.sln

• .NET Project Structure (David Fowler)
  https://gist.github.com/davidfowl/ed7564297c61fe9ab814

$/
  artifacts/
  build/
  docs/
  lib/
  packages/
  samples/
  src/
  tests/
  .editorconfig
  .gitignore
  .gitattributes
  build.cmd
  build.sh
  LICENSE
  NuGet.Config
  README.md
  {solution}.sln