Add nuget audit

[toddbaert]

.NET/NuGet offers great settings to prevent similar issues in the future. You can add

  <PropertyGroup>
    <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
    <NuGetAudit>true</NuGetAudit>
    <NuGetAuditMode>all</NuGetAuditMode>
    <NuGetAuditLevel>low</NuGetAuditLevel>
  </PropertyGroup>

to your global props file.

Originally posted by @Kielek in #347 (review)