Add better support for customizing SwaggerUI

[cguyonnet]

I wanted to define some ResponseInterceptor for SwaggerUI but it looked like these options were never actually set (cf. BuilderExtensions:InitUIOption()).

This PR aims at providing better control over SwaggerUI options by:

• decoupling SwaggerForOcelotUIOptions and SwaggerUIOptions
• adding a parameter to UseSwaggerForOcelotUI() to customize SwaggerUI