Test scenario form creating a custom field with empty name, other  for check how the fallback name is set.

Conflicts:

	spec/controllers/custom_fields_controller_spec.rb
Custom validator to check the presence of custom field name.

Conflicts:

	app/models/custom_field.rb
Add also validation for name value length
Acceptance tests for empty custom fields
Merge pull request #1367 from opf/release/fix/5652_custom_fields_with_empty_name

[Release][Fix] #5652: Custom fields with empty name can be created