Add Keywords key in desktop file

See:
- https://wiki.gnome.org/Initiatives/GnomeGoals/DesktopFileKeywords
- https://specifications.freedesktop.org/desktop-entry-spec/latest/ar01s05.html

desktop/colobot.ini

@@ -1,4 +1,4 @@
 Name="Colobot"
 GenericName="Game to learn programming"
 Comment="Colonize with bots"
-
+Keywords="robots;3d;space;astronaut;java;c++"

desktop/create_desktop_file.sh

@@ -10,7 +10,7 @@ cat colobot.desktop.in
 
 linguas=$([ ! -d lang ] || ( cd lang ; ls));
 
-for type in Name GenericName Comment; do
+for type in Name GenericName Comment Keywords; do
     egrep "^$type=" $fname | sed -e "s/^$type=\"\(.*\)\"$/$type=\1/g"
     for l in $linguas; do
         egrep "^$type=" lang/$l/$fname | sed -e "s/^$type=\"\(.*\)\"$/$type[$l]=\1/g"

desktop/po/colobot-desktop.pot

@@ -7,7 +7,7 @@
 msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
-"POT-Creation-Date: 2016-03-25 19:24+0100\n"
+"POT-Creation-Date: 2016-03-30 13:45+0200\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -34,6 +34,12 @@ msgstr ""
 msgid "Colonize with bots"
 msgstr ""
 
+#. type: Keywords=
+#: colobot.ini:4
+#, no-wrap
+msgid "robots;3d;space;astronaut;java;c++"
+msgstr ""
+
 #. type: =head1
 #: colobot.pod:3
 msgid "NAME"

desktop/po/fr.po

@@ -6,8 +6,8 @@
 msgid ""
 msgstr ""
 "Project-Id-Version: colobot 0.1.7\n"
-"POT-Creation-Date: 2016-03-25 19:24+0100\n"
-"PO-Revision-Date: 2016-03-25 21:13+0100\n"
+"POT-Creation-Date: 2016-03-30 13:45+0200\n"
+"PO-Revision-Date: 2016-03-30 13:49+0100\n"
 "Last-Translator: Didier Raboud <odyx@debian.org>\n"
 "Language: fr\n"
 "MIME-Version: 1.0\n"
@@ -34,6 +34,12 @@ msgstr "Apprentissage de la programmation par le jeu"
 msgid "Colonize with bots"
 msgstr "Colonise avec des roBots"
 
+#. type: Keywords=
+#: colobot.ini:4
+#, no-wrap
+msgid "robots;3d;space;astronaut;java;c++"
+msgstr "robots;3d;espace;astronaute;cosmonaute;java;c++"
+
 #. type: =head1
 #: colobot.pod:3
 msgid "NAME"