[Core] Adds server side validation to multi file upload elements.

(refs #5434, gh-46)
[Applications] Adds server side validation to attachments form element.

+ Prepares configuration via config array and build process.

(refs #5434, gh-46)
[Auth] Prepares form configuration via build process.

- removes file upload config for user image from module.config.
- adds this config to auth.forms.global.php.dist (used in the build process)

(refs #5434, gh-46)
(General) Integrates file upload formular validation configuration in the build process.

(refs #5434, gh-46)