Move languages to standard LINGUAS file

This is necessary for other translation tools to work properly.

po/CMakeLists.txt

@@ -1,8 +1,6 @@
 # Gettext support - mostly borrowed from the Licq project
 
-set(po_FILES
-    bg da de el eo es fi fr fur hu it nl pl pt_BR ru sk sr sv tr uk vi zh_CN
-)
+file(STRINGS LINGUAS po_FILES)
 
 if (NOT GETTEXT_MSGMERGE_EXECUTABLE AND NOT GETTEXT_MSGFMT_EXECUTABLE)
   message(FATAL_ERROR "Gettext message catalog tools NOT found")

po/LINGUAS

@@ -0,0 +1,22 @@
+bg
+da
+de
+el
+eo
+es
+fi
+fr
+fur
+hu
+it
+nl
+pl
+pt_BR
+ru
+sk
+sr
+sv
+tr
+uk
+vi
+zh_CN