Support collection translations with lambdas for collection input

This allows to use dynamically generated translations.

It's pretty rarely needed thing, I think.

For example, I use this to DRY in translations (ability names was translated before):

```ruby
{ ru: {
    simple_form: {
      options: {
        rank: {
          abilities: Hash[
            ABILITIES.map do |ability|
              [ability.to_sym, -> (*) { I18n.t(ability, scope: :abilities) }]
            end
          ]
}, }, }, }, }
```

Also, I'm currently passing translated key and input option to Proc in translations, but not sure, should it be ever passed. Can't imagine use cases, just mimics rails validators in behavior (rails passes attribute name and validator arguments to translation). So, further discussion is required.