Fixed MSVC warnings.

warning C4099: 'ESM::ESMReader' : type name first seen using 'class' now seen using 'struct'
warning C4099: 'ESM::CellId' : type name first seen using 'struct' now seen using 'class'

apps/essimporter/importacdt.hpp

@@ -9,7 +9,7 @@
 
 namespace ESM
 {
-    struct ESMReader;
+    class ESMReader;
 }
 
 namespace ESSImport

apps/essimporter/importdial.hpp

@@ -2,7 +2,7 @@
 #define OPENMW_ESSIMPORT_IMPORTDIAL_H
 namespace ESM
 {
-    struct ESMReader;
+    class ESMReader;
 }
 
 namespace ESSImport

apps/essimporter/importinfo.hpp

@@ -5,7 +5,7 @@
 
 namespace ESM
 {
-    struct ESMReader;
+    class ESMReader;
 }
 
 namespace ESSImport

apps/essimporter/importjour.hpp

@@ -5,7 +5,7 @@
 
 namespace ESM
 {
-    struct ESMReader;
+    class ESMReader;
 }
 
 namespace ESSImport

apps/essimporter/importklst.hpp

@@ -6,7 +6,7 @@
 
 namespace ESM
 {
-    struct ESMReader;
+    class ESMReader;
 }
 
 namespace ESSImport

apps/essimporter/importques.hpp

@@ -6,7 +6,7 @@
 
 namespace ESM
 {
-    struct ESMReader;
+    class ESMReader;
 }
 
 namespace ESSImport

components/esm/loadcell.hpp

@@ -18,7 +18,7 @@ namespace ESM
 {
 class ESMReader;
 class ESMWriter;
-    class CellId;
+struct CellId;
 
 /* Moved cell reference tracking object. This mainly stores the target cell
         of the reference, so we can easily know where it has been moved when another