flatpak: Allow dual installation of app bundles

Part of https://gitlab.gnome.org/GNOME/Initiatives/issues/1.
Allows for the installation of development bundles alongside
stable versions.

Related to https://gitlab.gnome.org/GNOME/gnome-calendar/issues/285

data/org.gnome.Calendar.desktop.in.in

@@ -0,0 +1,13 @@
+[Desktop Entry]
+Name=Calendar
+Comment=Access and manage your calendars
+Exec=gnome-calendar
+# Translators: Do NOT translate or transliterate this text (this is an icon file name)!
+Icon=@icon@
+Terminal=false
+Type=Application
+StartupNotify=true
+Categories=GNOME;GTK;Office;Calendar;Core;
+# Translators: Search terms to find this application. Do NOT translate or localize the semicolons! The list MUST also end with a semicolon!
+Keywords=Calendar;Event;Reminder;
+DBusActivatable=true