Switch to side-by-side view

--- a/src/qtgui/recoll.pro.in
+++ b/src/qtgui/recoll.pro.in
@@ -26,6 +26,8 @@
         idxsched.h \
         listdialog.h \
         preview_w.h \
+        preview_load.h \
+        preview_plaintorich.h \
         ptrans_w.h \
         rclhelp.h \
         rclmain_w.h \
@@ -52,6 +54,8 @@
         main.cpp \
         multisave.cpp \
         preview_w.cpp \
+        preview_load.cpp \
+        preview_plaintorich.cpp \
         ptrans_w.cpp \
         rclhelp.cpp \
         rclmain_w.cpp \