Additional encoding of legal basis, in addition to `epo:hasLegalBasis` on Notice.

[csnyulas]

This is an issue created to deal with the open questions left on issue 349: #349 (comment)

In summary, after the adding the epo:hasLegalBasis property to the Notice instead of the Procedure, as requested n #349, the following questions came up:

• Does this mean that in the RDF data the epo:Procedure will never have the legal-basis set?
• How is the epo:isBasedOnImplementingRegulation property to be used? Wouldn't that be (more) appropriate (or at least in certain situations) to be used on the notice, as that represents the selection of the legal basis on the Standard Form, referring to the legal base on which the form used for that given notice was created?
• How about the LEGAL_BASIS_OTHER xml element, which at the moment is not mapped, as we don't have appropriate property and (controlled) value set? Would that also be added to the epo:Notice (and only to the Notice) later?