"Tux Paint (Fullscreen)" launcher for Freedesktop.org

Adding a separate launcher that runs "tuxpaint --fullscreen=native"
for XDG environments (e.g., Linux); similar to what we have for
Windows.

Closes https://sourceforge.net/p/tuxpaint/feature-requests/227/
h/t Aaron

src/po/ca.po

@@ -17,7 +17,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: Tuxpaint cvs 2009-06-21\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2023-03-30 09:13-0700\n"
+"POT-Creation-Date: 2023-04-01 16:47-0700\n"
 "PO-Revision-Date: 2023-03-30 23:09+0200\n"
 "Last-Translator: Pere Pujal i Carabantes <perepujal@gmail.com>\n"
 "Language-Team: Català <linux-ca@chanae.alphanet.ch>\n"
@@ -359,6 +359,7 @@ msgid "Tux Paint"
 msgstr "Tux Paint"
 
 #: ../org.tuxpaint.Tuxpaint.appdata.xml.in:9 ../tuxpaint.desktop.in:10
+#: ../tuxpaint-fullscreen.desktop.in:10
 msgid "A drawing program for children"
 msgstr "Un programa de dibuix per a nens petits"
 
@@ -1498,10 +1499,14 @@ msgstr ""
 "Feu clic en els colors primaris(magenta, groc i cian), blanc (per aclarir), "
 "gris, o negre(per enfosquir), per barrejar-los en un color nou."
 
-#: ../tuxpaint.desktop.in:9
+#: ../tuxpaint.desktop.in:9 ../tuxpaint-fullscreen.desktop.in:9
 msgid "Drawing program"
 msgstr "Programa de dibuix"
 
+#: ../tuxpaint-fullscreen.desktop.in:3
+msgid "Tux Paint (Fullscreen)"
+msgstr ""
+
 #: ../../magic/src/alien.c:67
 msgid "Color Shift"
 msgstr "Altera colors"