Support optionsetfield properly and add min/max check constraint

Hi,

regarding this issue https://github.com/sheadawson/silverstripe-zenvalidator/issues/15 I have updated to code to support the optionset properley.

The issue is that no attributes are set on the input (radio or checkboxes). To fix this, I simply override the optionsetfield_holder.ss template and expose the attributes there. Then, before initializing parsley, I apply the parsley data attributes through javascript.

Works good on my side, I hope you like the way I implemented this. I will also open an issue on the framework repos because there are really no reason to not expose the attributes on optionsetfield_holder.ss for everyone.