Allow to add concerns via framework convenience methods

[Kaliumhexacyanoferrat]

As a developer of a web service application, I would like to be able to pass concerns to framework convenience calls, so that I do not need to create an additional layout.

Probably related to #750.

Example

Inline.Create()
      .Get(() => ...)
      .Post(() => ..., MyConcern.Create());

Acceptance criteria

• All framework methods allow to add one or more concerns directly in the registration
• The feature is documented on the GenHTTP website
• The feature is covered by acceptance tests