panels: Add keywords to all the panels we ship

https://bugzilla.gnome.org/show_bug.cgi?id=399754

examples/gnome-example-panel.desktop.in.in

@@ -6,6 +6,9 @@ Icon=application-x-executable
 Terminal=false
 Type=Application
 StartupNotify=true
-Categories=GNOME;GTK;Settings;DesktopSettings;
+# The X-GNOME-Settings-Panel is necessary to show in the main shell UI
+Categories=GNOME;GTK;Settings;DesktopSettings;X-GNOME-Settings-Panel;
 OnlyShowIn=GNOME;
 X-GNOME-Settings-Panel=example-panel
+# Translators: those are keywords for the example control-center panel
+_X-GNOME-Keywords=Foo;Bar;Baz;

panels/background/gnome-background-panel.desktop.in.in

@@ -9,3 +9,5 @@ StartupNotify=true
 Categories=GNOME;GTK;Settings;DesktopSettings;X-GNOME-Settings-Panel;
 OnlyShowIn=GNOME;
 X-GNOME-Settings-Panel=background
+# Translators: those are keywords for the background control-center panel
+_X-GNOME-Keywords=Wallpaper;Screen;

panels/datetime/gnome-datetime-panel.desktop.in.in

@@ -9,3 +9,5 @@ StartupNotify=true
 Categories=GNOME;GTK;Settings;X-GNOME-SystemSettings;X-GNOME-Settings-Panel;
 OnlyShowIn=GNOME;
 X-GNOME-Settings-Panel=datetime
+# Translators: those are keywords for the date and time control-center panel
+_X-GNOME-Keywords=Clock;Timezone;Location;

panels/display/gnome-display-panel.desktop.in.in

@@ -14,4 +14,4 @@ X-GNOME-Bugzilla-Component=Screen resolution
 X-GNOME-Bugzilla-Version=@VERSION@
 X-GNOME-Settings-Panel=display
 # Translators: those are keywords for the display control-center panel
-_X-GNOME-Keywords=Panel;Projector;xrandr;screen;
+_X-GNOME-Keywords=Panel;Projector;xrandr;Screen;Resolution;Refresh;

panels/keyboard/gnome-keyboard-panel.desktop.in.in

@@ -13,3 +13,5 @@ X-GNOME-Bugzilla-Product=gnome-control-center
 X-GNOME-Bugzilla-Component=keyboard
 X-GNOME-Bugzilla-Version=@VERSION@
 X-GNOME-Settings-Panel=keyboard
+# Translators: those are keywords for the keyboard control-center panel
+_X-GNOME-Keywords=Shortcut;Repeat;Blink;

panels/mouse/gnome-mouse-panel.desktop.in.in

@@ -13,3 +13,5 @@ X-GNOME-Bugzilla-Product=gnome-control-center
 X-GNOME-Bugzilla-Component=mouse
 X-GNOME-Bugzilla-Version=@VERSION@
 X-GNOME-Settings-Panel=mouse
+# Translators: those are keywords for the mouse and touchpad control-center panel
+_X-GNOME-Keywords=Trackpad;Pointer;Click;Tap;Double;Button;

panels/network/gnome-network-panel.desktop.in.in

@@ -13,3 +13,5 @@ X-GNOME-Bugzilla-Product=gnome-control-center
 X-GNOME-Bugzilla-Component=network preferences
 X-GNOME-Bugzilla-Version=@VERSION@
 X-GNOME-Settings-Panel=network
+# Translators: those are keywords for the network proxy control-center panel
+_X-GNOME-Keywords=Web;Location;

panels/region/gnome-region-panel.desktop.in.in

@@ -13,3 +13,5 @@ X-GNOME-Bugzilla-Product=gnome-control-center
 X-GNOME-Bugzilla-Component=region
 X-GNOME-Bugzilla-Version=@VERSION@
 X-GNOME-Settings-Panel=region
+# Translators: those are keywords for the region control-center panel
+_X-GNOME-Keywords=Language;Layout;

panels/screen/gnome-screen-panel.desktop.in.in

@@ -13,3 +13,5 @@ X-GNOME-Bugzilla-Product=gnome-control-center
 X-GNOME-Bugzilla-Component=screen
 X-GNOME-Bugzilla-Version=@VERSION@
 X-GNOME-Settings-Panel=screen
+# Translators: those are keywords for the brightness and lock control-center panel
+_X-GNOME-Keywords=Brightness;Lock;Dim;Blank;

panels/sound/data/gnome-sound-panel.desktop.in.in

@@ -13,3 +13,5 @@ X-GNOME-Bugzilla-Product=gnome-control-center
 X-GNOME-Bugzilla-Component=sound
 X-GNOME-Bugzilla-Version=@VERSION@
 X-GNOME-Settings-Panel=sound
+# Translators: those are keywords for the sound control-center panel
+_X-GNOME-Keywords=Card;Microphone;Volume;Fade;Balance;Bluetooth;Headset;

panels/universal-access/gnome-universal-access-panel.desktop.in.in

@@ -13,3 +13,5 @@ X-GNOME-Bugzilla-Product=gnome-control-center
 X-GNOME-Bugzilla-Component=Universal Access
 X-GNOME-Bugzilla-Version=@VERSION@
 X-GNOME-Settings-Panel=universal-access
+# Translators: those are keywords for the universal access control-center panel
+_X-GNOME-Keywords=Keyboard;Mouse;a11y;Accessibility;

panels/user-accounts/data/gnome-user-accounts-panel.desktop.in.in

@@ -13,3 +13,5 @@ X-GNOME-Bugzilla-Product=gnome-control-center
 X-GNOME-Bugzilla-Component=user-accounts
 X-GNOME-Bugzilla-Version=@VERSION@
 X-GNOME-Settings-Panel=user-accounts
+# Translators: those are keywords for the user accounts control-center panel
+_X-GNOME-Keywords=Login;Name;Fingerprint;Avatar;Logo;Face;Password;