Fix build against exiv2-0.27.1 by using upstream recommended catchall header.

--- a/src/hugin_base/panodata/SrcPanoImage.cpp	2019-02-16 09:18:55.000000000 +0100
+++ b/src/hugin_base/panodata/SrcPanoImage.cpp	2019-05-21 14:26:23.470193305 +0200
@@ -40,9 +40,7 @@
 #include <vigra/diff2d.hxx>
 #include <vigra/imageinfo.hxx>
 #include <hugin_utils/utils.h>
-#include <exiv2/exif.hpp>
-#include <exiv2/image.hpp>
-#include <exiv2/easyaccess.hpp>
+#include <exiv2/exiv2.hpp>
 #include <lensdb/LensDB.h>
 #include "Exiv2Helper.h"
 
--- a/src/hugin1/hugin/RawImport.cpp	2019-02-02 11:11:01.000000000 +0100
+++ b/src/hugin1/hugin/RawImport.cpp	2019-05-21 14:33:00.522541182 +0200
@@ -35,10 +35,7 @@
 // workaround for a conflict between exiv2 and wxWidgets/CMake built
 #define HAVE_PID_T 1
 #endif
-#include <exiv2/exif.hpp>
-#include <exiv2/image.hpp>
-#include <exiv2/easyaccess.hpp>
-#include <exiv2/xmpsidecar.hpp>
+#include <exiv2/exiv2.hpp>
 #ifdef __WXMSW__
 #include <wx/msw/registry.h>
 #endif