- added initial draft for third party sql checker support

src/ClientServer/Config/Constants.cs

src/ClientServer/Config/InitialSystemSettings.cs

...ollers/Core/CustomProjects/EditCustomProjectController.cs

...xerciseAfterSolution/DoExerciseAfterSolutionController.cs

...Server/Controllers/Core/Exercises/DoExerciseController.cs

...er/Controllers/Core/Exercises/ExerciseEditorController.cs

src/ClientServer/Controllers/Core/Init.cs

...ClientServer/Controllers/Core/SystemSettingsController.cs

...lientServer/Controllers/Core/Testing/TestingController.cs

...r/Controllers/Core/Testing/ThirdParty/SqlCheckerHelper.cs

...grations/20200125155006_SqlCheckerIntegration.Designer.cs

...Server/Migrations/20200125155006_SqlCheckerIntegration.cs

...73731_ThirdPartySqlCheckerUrlInSystemSettings.Designer.cs

...20200201173731_ThirdPartySqlCheckerUrlInSystemSettings.cs

src/ClientServer/Migrations/YapexDbContextModelSnapshot.cs

src/ClientServer/Models/CustomProjects/CustomProjectTest.cs

.../Exercises/Solution/TestWithSingleSolutionAsTestResult.cs

src/ClientServer/Models/Exercises/Tests/CustomTest.cs

src/ClientServer/Models/Exercises/Tests/Test.cs

src/ClientServer/Models/Interfaces/AllTest.cs