added articleclass for letter, preprint, final

New argument makes the main file easier to use in order to differentiate between preprint, final version and letter (data management letter).

final.def

@@ -5,10 +5,10 @@
 		\begin{flushleft}%
 			\normalsize\sffamily%
 			{\normalsize\MakeUppercase{\@articletype}\par}
-			\ifletter
+			\ifx\@articleclass\letter
 			\marginnote{\includegraphics[width=\linewidth]{./logos/inggrid.pdf}}%[.5\baselineskip]
 			\else
-			\iffinal
+			\ifx\@articleclass\final
 			\marginnote{\includegraphics[width=\linewidth]{./logos/inggrid.pdf}}%[.5\baselineskip]
 			\else
 			\marginnote{\includegraphics[width=\linewidth]{./logos/inggrid-preprints.pdf}}%[.5\baselineskip]
@@ -30,13 +30,13 @@
 		\vskip 2ex
 	}
     \sideinfofield{Date Submitted}{datesubmitted}
-	\ifletter
+	\ifx\@articleclass\letter
 	\sideinfofield{Date Published}{datepublished}
 	\sideinfofield{DOI}{doi}
 	\sideinfofield{License}{licenses}
     \sideinfofield{Keywords}{keywords}
 	\else
-	\iffinal
+	\ifx\@articleclass\final
 	\sideinfofield{Date Received}{datereceived}
 	\sideinfofield{Date Accepted}{dateaccepted}
 	\sideinfofield{Date Published}{datepublished}