Confirmable passwords and persist old input

Entrust GUI now uses Esensi/Model which allows for more complex validation and moves password hashing to the User model. This allows for optional confirmable passwords.

Because hashing passwords moves from the package to the model it's essential that models are updated. For this reason using the previously recommended model will now throw an exception

User model must implement Esensi\Model\Contracts\HashingModelInterface. Revert to 0.3.* or see upgrade guide for details.

This is to prevent passwords being saved unhashed and force users to either revert or comply to the changes.

This release also persists old input when validation fails and tidies up spacing issues with various buttons.