Add auto finding of sun-safe home

[mmccrackan]

This branch uses the existing sun-safe parking function to try and find a sun-safe home position automatically if the stow_position dict is empty or None. It will search at az=180 and between el=60 and el=sun_policy['min_el'] for a stow position. If az_stow and el_stow are given in the config, those values are used instead and no calculation is done (in case we want to override it for some reason), though we could eliminate them from the config entirely and only use the calculated ones if we wanted to.