nm: Add AppStream metadata

This will ensure the strongSwan NetworkManager plugin will be easily
installable from the app stores such as GNOME Software.

Closes strongswan/strongswan#41.

src/frontends/gnome/Makefile.am

@@ -10,6 +10,11 @@ nmvpnservice_DATA = nm-strongswan-service.name
 
 @INTLTOOL_DESKTOP_RULE@
 
+appdatadir = $(datadir)/appdata
+appdata_DATA = $(appdata_in_files:.xml.in=.xml)
+appdata_in_files = NetworkManager-strongswan.appdata.xml.in
+@INTLTOOL_XML_RULE@
+
 nm-strongswan-service.name: $(srcdir)/nm-strongswan-service.name.in
 	$(AM_V_GEN) \
 	sed -e 's|[@]LIBEXECDIR[@]|$(libexecdir)|' \
@@ -17,11 +22,13 @@ nm-strongswan-service.name: $(srcdir)/nm-strongswan-service.name.in
 
 EXTRA_DIST = nm-strongswan-service.name.in \
     $(dbusservice_DATA)  \
+    $(appdata_in_files)  \
+    $(appdata_DATA)      \
     intltool-extract.in  \
     intltool-merge.in    \
     intltool-update.in
 
-CLEANFILES = $(nmvpnservice_DATA) *~
+CLEANFILES = $(nmvpnservice_DATA) $(appdata_DATA) *~
 DISTCLEANFILES = intltool-extract intltool-merge intltool-update
 
 ACLOCAL_AMFLAGS = -I m4