Use the site name in opengraph tags

…which involves passing around the index file to a lot more places

Makefile

@@ -147,17 +147,19 @@ endef
 
 # args:
 #  1. gallery prefix
-#  2. build dir
-#  3. data dir
-#  4. other flags
+#  2. index filename
+#  3. build dir
+#  4. data dir
+#  5. other flags
 define depend-single
 echo "[deps]    "$@
 mkdir -p "$(dir $@)"
-$(MAKEPAGES) $(MPFLAGS) depend-single $(4) \
+$(MAKEPAGES) $(MPFLAGS) depend-single $(5) \
   --output "$@" \
   --prefix "$(1)" \
-  --build-dir "$(2)" \
-  --data-dir "$(3)" $<
+  --index "$(2)" \
+  --build-dir "$(3)" \
+  --data-dir "$(4)" $<
 endef
 
 # args
@@ -178,14 +180,16 @@ endef
 # args:
 #  1. data dir
 #  2. gallery prefix
-#  3. other flags
+#  3. index file
+#  4. other flags
 define single
 echo "[single]  "$@
 mkdir -p "$(dir $@)"
-$(MAKEPAGES) $(MPFLAGS) single $(3) \
+$(MAKEPAGES) $(MPFLAGS) single $(4) \
   --root $(ROOT) \
   --data-dir "$(1)" \
   --prefix "$(2)" \
+  --index "$(3)" \
   --output "$@" \
   $<
 endef