Doublechecking Editorial Notes and NOTEs

[riccardoAlbertoni]

closing #1518

[riccardoAlbertoni]

This Pr deletes or modifies the (editor's) notes. The rationale is

• removing any stale editor's note which pertained to previous stages, such as the publication of previous working notes for DCAT 3 ( e.g. we've dropped "This is the usage note in [[?DCAT-AP]]. To be decided if it should be adopted in DCAT.");
• maintains information about when the features have been added and why (Eg. "Property added in this context in DCAT X. see issue yyyy" );
• maintaining comments referring to features added in a previous version of DCAT if they help to understand the DCAT evolution.
• Some notes have been rephrased: "For DCAT 2, this was generalized, and properties common to all catalogued resources were associated with a super-class dcat:Resource" has become "Since DCAT 2 [[?VOCAB-DCAT-2]] ... "
• we've kept the EDITOR's note about RDF serialization as the RDF files are in the github repo till the DCAT does not hit the REC status;