refactor($core): extract naming and labels methods in mixins
feat($core): implements wrappers for inputs and actions
feat(inputs): adds blocks support in inputs method

Passing a block to the `inputs` method appends the block
result to the field set wrapper. Both symbols and a block
can be passed to `inputs` at the same time.
feat(inputs): adds legend support for inputs fieldsets
feat(inputs): adds `_input`suffix to inputs id