* GetDateTimeFormatterField
** a FieldReference that creates DateTimeFormatters
   for given dateFormat as mapper fields
** variableName is created using given dateFormat

* AbstractJavaTimeToStringConversion
  provides GetDateTimeFormatterField as required helper field
  using DateTimeFormatter instances provided as mapper fields
  by GetDateTimeFormatterField

* ConversionProvider
  might provide supporting fields directly

* Refactoring
  moved/renamed BuiltInFieldReference, BuiltInConstuctorFragment to
package model/common

* MappingBuilderContext provides access to mapper support fields
  (that are independent of mapper methods)

* MappingResolverImpl / MapperCreationProcessor
  process supporting fields provided by ConversionProvider

* HelperMethod
** extended to supply additional template parameters to
   be more flexible in freemarker templates
** extended to support mapper field reference / constructor fragment

* SupportingMappingMethod
** provide templateParameters to freemarker
** hashCode/equals base on name property instead of template name,
   as we use one specific template multiple times with different
   parameters generating multiple methods
** #getSafeField extracted to SupportingField

* SupportingField
** removed hashCode/equals based on template name,
   as we use one specific template multiple times with different
   parameters generating multiple methods
   (superclass equals/hashcode is fine for that)
** added support for template parameters to be more flexible when
  compiling templates

* Tests to verify DateTimeFormatter instance field creation