Allow global configuration of the default value for ngMessages' multiple

[realityking]

In a large application with hundereds of form fields it's rather tedious to always remember to add ng-messages-multiple to get a consistent expierence for users.

It would be great if a default could be set globally. This might entail changing ng-messages-multiple to accept an expression (or a string) to allow disabling it when the default is to show multiple messages.

[Narretz]

Sounds reasonable. Feedback / PR welcome.

[kentcdodds]

I think this feature would definitely be handy.

I want to mention angular-formly. Disclosure, it's my library, so feel free to take this with a grain of salt. But making this happen with angular-formly would be trivial using the wrappers feature. I threw together a quick example. Hopefully this is more helpful than spammy.