MSBuild generation: incremental build and clean rebuild improvements

[DanielTheCoder]

Several improvements for current MSBuild based code-behind files generation

• Try to fix incremental build issue inside visual studio 2017 if feature file changed outside of visual studio
  • typically you'll see the message 'target skipped because of no input files changed'
  • this fix should also work more reliable if using MSBuild from command line
  • this fix should also improve compatibility with new sdk based MSBuild projects
• add experimental support for deleting code-behind files on clean or rebuild
  • to use code-behind file deletion you'll have to set the MSBuild property 'SpecFlow_DeleteCodeBehindFilesOnCleanRebuild' to 'true' inside your csproj or using on of the directory or solution extension points in MSBuild https://docs.microsoft.com/en-us/visualstudio/msbuild/customize-your-build
• removed unused MSBuild property 'OnlyUpdateIfChanged'

Types of changes

• Bug fix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as expected).

Checklist:

• I've added tests for my code.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added an entry to the changelog