datetime: Use '&' instead of 'and'

Using "&" not only keeps the names shorter but would also keeps the
user focused on the other words which compose the name.

https://bugzilla.gnome.org/show_bug.cgi?id=676562

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

@@ -1,5 +1,5 @@
 [Desktop Entry]
-_Name=Date and Time
+_Name=Date & Time
 _Comment=Date and Time preferences panel
 Exec=gnome-control-center datetime
 Icon=preferences-system-time