[Xfce-i18n] Fill po headers (PACKAGE VERSION) to avoid msgfmt warnings

[scootergrisen]

I download po files from Transifex and check them with msgmft -cv.

Some files gives warning because the header is not filled:
"Project-Id-Version: PACKAGE VERSION\n"

Can someone make sure they are get filled in the future so we can avoid 
the warnings.

The files are:
xfce-apps.catfish
xfce-apps.xfce4-panel-profiles
xfce-apps.xfce4-screensaver
xfce-panel-plugins.xfce4-calculator-plugin
xfce-panel-plugins.xfce4-sample-plugin

Comparing with the other files it seems they should contain:
Project-Id-Version: Xfce Apps\n"
Project-Id-Version: Xfce Apps\n"
Project-Id-Version: Xfce Apps\n"
Project-Id-Version: Xfce Panel Plugins\n"
Project-Id-Version: Xfce Panel Plugins\n"

Here are all the "Project-Id-Version" lines from all the po files in 
case its usefull.

Project-Id-Version: PACKAGE VERSION\n"
Project-Id-Version: Exo\n"
Project-Id-Version: Garcon\n"
Project-Id-Version: Libxfce4ui\n"
Project-Id-Version: Libxfce4util\n"
Project-Id-Version: Thunar Plugins\n"
Project-Id-Version: Thunar-volman\n"
Project-Id-Version: Thunar\n"
Project-Id-Version: Tumbler\n"
Project-Id-Version: Xfce Apps\n"
Project-Id-Version: Xfce Panel Plugins\n"
Project-Id-Version: Xfce4-appfinder\n"
Project-Id-Version: Xfce4-panel\n"
Project-Id-Version: Xfce4-power-manager\n"
Project-Id-Version: Xfce4-session\n"
Project-Id-Version: Xfce4-settings\n"
Project-Id-Version: xfce4-statusnotifier-plugin\n"
Project-Id-Version: Xfconf\n"
Project-Id-Version: Xfdesktop\n"
Project-Id-Version: Xfwm4\n"