Reworked referencenumber adapter, for make it easier to customize and use it in the treeportlet.
Implements different customizable reference_number_formatter
Added upgrade step which initialize the ReferenceNumber Formatters.
Made referncenumber prefix starting point customizable in registry.
Fixed docstring.
Merge pull request #112 from 4teamwork/pg_reference_number_rebuild

Dynamic format for repository reference numbers.