Use a builder pattern for configuring options in UseDatabaseErrorPage

[Eilon]

There's a general pattern where types that are used only for configuring middleware also end up in the Microsoft.AspNet.Builder namespace, alongside the various app.UseXyz(...) extension methods.

The DatabaseErrorPageOptions is used only in middleware setup (and effectively internally elsewhere), so it should move to the Microsoft.AspNet.Builder namespace.

The end result is that fewer namespaces need to be imported in a typical Startup.cs file.

[Eilon]

Just discussed another option with @Tratcher that both of us like:

Instead of passing in a particular type, the UseXyz() method to add the middleware could use a builder pattern and take in options that are configured inline, removing the need to reference any type by name at all, e.g.:

app.UseDatabaseErrorPage(options => {
    options.ShowExceptionDetails = true;
    options.ListMigrations = true;
});

Or if that's too verbose, could add a helper:

app.UseDatabaseErrorPage(options => {
    options.EnableAll(); // just sets all the properties to true
});

This would be even more inline with how other middleware works, as seen here: https://github.com/aspnet/MusicStore/blob/dev/src/MusicStore/Startup.cs#L161-L218

[Eilon]

@rynowak FYI

[rowanmiller]

Agreed on the builder pattern. I working on #190 at the moment so I will enable this pattern at the same time.

[Eilon]

@rowanmiller cool.

[rowanmiller]

Fixed in 1c26436

[Eilon]

@rowanmiller remember to mark completed bugs as 3 - Done.

[rowanmiller]

@Eilon done... I mean 3 - Done

[Eilon]

4 - Thanks!