Add more things for customising error messages

[GooRiOn]

I'd be cool if we could add more things for customising error messages. I thought about something very simple like "tokens" which we could put into the string which then would be replaced with something like "{displayName} is required". I thought about the following tokens:

• propertyName
• displayName
• value

The above would imply adding new extension method - WithDisplayName()

[timdeschryver]

Maybe something else to add would be to override the default messages? (Having localization in mind)
Perhaps this a separate issue tho...

[dbarwikowski]

What about cases where we compare two properties of model

"'EndDate' must be later than 'StartDate'"