[fj-doc-mod-fop] add pdf/a support

[fugerit79]

Adding support for pdf/a format.

The concept of format has been introduced.
By default the format is the same as the type (pdf, xlsx, html etc).

It is possible now to add format for the same type.

The DocHandlerFacade can handle multiple handlers for the same type, as long as the format is diffirent.

For instance we can have a normal pdf handler (type : pdf, format : pdf) and a pdf a handler (type : pdf, format : PDF/A-1a).

An example in the fj-doc-sample project will be provided.