Changes to ScalaForms documentation

General rewrite of ScalaForms.  This PR is based off master and is appropriately squashed.

Added a list of Forms mapping.
Added list of helpers.
Add diagram showing form handling flow (using draw.io format)
Merged ScalaFormHelpers.md into ScalaForms to show helper usage directly with the form mapping.
Added a ScalaCustomValidations.md file to show how to create custom constraints.
Moved the Custom Field Validations section out to its own file.
Added links for everything.