split ItemID into categories

src/mslinks/LinkTargetIDList.java

src/mslinks/ShellLinkHelper.java

src/mslinks/UnsupportedItemIDException.java

src/mslinks/data/ItemID.java

src/mslinks/data/ItemIDDrive.java

src/mslinks/data/ItemIDFS.java

src/mslinks/data/ItemIDRoot.java

src/mslinks/data/ItemIDUnknown.java