Support named actions

PDFBox does not support named actions, see this question:
https://stackoverflow.com/questions/28060866/

The user has this code

<< /Type /Annot /Subtype /Link /Rect [0.0 0.0 100.0 100.0] /H /P /BS 1049 0 R /A 1050 0 R >>

1050 0 obj <</N /GoBack /S /Named>>

The solution is to derive a new class from PDAction and also to change to PDActionFactory.