Mark AddNLog-methods as obsolete and instead redirect to AddNLogWeb

[snakefoot]

Keep users from thinking that they need to call both:

builder.AddNLog()
builder.AddNLogWeb()

Avoid naming confusion with extension-methods from NLog.Extensions.Logging. Making it easier to explain users that they should always use AddNLogWeb() for ASP.NET Core applications.

[bakgerman]

Completed this in a branch until ready for merge