Friendly exceptions for dictionary mapping errors

[tpluscode]

Romantic Web uses a Fody plugin to generate entity types for IList/ICollection and IDictionary mappings.

Unfortunately when RomanticWeb.Fody package is not installed or the ForyWeaver.xml isn't complete those type will not be produced, which in turn will cause obscure exceptions. They should be caught and replaced with a more informative errors

• check for errors during mapping of dictionaries and collections
• create a documentation page describing whan can be done
• thrown an exception with a link to the documentation