Start up in daemon mode when GNOME starts

Hat tip to Guido for the session.{c,h} files.

Closes #45

data/sm.puri.Calls-daemon.desktop

@@ -0,0 +1,16 @@
+[Desktop Entry]
+Name=Calls (daemon)
+GenericName=Phone
+Comment=A phone dialer and call handler (daemon mode)
+# Translators: These are desktop search terms. Do not translate semicolons, end line with a semicolon.
+Keywords=Telephone;Call;Phone;Dial;Dialer;PTSN;
+# Translators: Do NOT translate or transliterate this text (this is an icon file name)!
+Icon=sm.puri.Calls
+TryExec=calls
+Exec=calls --daemon
+Type=Application
+StartupNotify=true
+NoDisplay=true
+Terminal=false
+Categories=GNOME;GTK;Telephony;
+X-GNOME-AutoRestart=true