Added VAT identification number validation

VATIN validation was added to the signer entity
Validation SuccessUrl

* Added successUrl parameter to validation entity
Preliminary folder entity

* Adding and removing case files from folders is not available yet
Add and remove case files

* Case files can now be added to and removed from folders
Added type templates

* Type templates are now available through the API for case files, documents and signers
Added access control for signing requests

* Each signing request can now be protected by either VAT identification number and/or social security number checks
Added custom validation text

* A custom text can be set on each validation in order to customize the message displayed to the user on the validation page
Validation reminders added

* Reminder functionality for validations were added
Updated documentation
Fixed error in documentation
Fixed typos
Merge branch 'development'