color-manager: Apply temperature after gsd.Color proxy has been created
Previously, restarting mutter in an X11 session resulted in
the previously set color temperature not being applied.
Fix that by applying the color temperature right after
the org.gnome.SettingsDaemon.Color proxy has been created.
Furthermore, only call `update_all_gamma()` from `on_gsd_color_ready()`
when the temperature has actually changed. Otherwise there is no need
since the current temperature has already been (or will soon be) applied
to all ready color devices.
Edited by Barnabás Pőcze