Allow specification of bright star by coordinates in `autofocus` and `align_guidescope`

[bgottula]

Currently it's only possible to specify what bright star to use in autofocus and align_guidescope by providing the name of that star. This interface is not very flexible and there are some moderately bright stars that don't have common names. A challenge for these specific programs is that program arguments for the target must be passed from a parent process (e.g., autofocus) to a subprocess (track).

• Modify these programs such that it's possible to specify a star using either a common name or equatorial coordinates.
• Add an enum.Flag parameter to targets.add_program_arguments() that allows the caller to pick a subset of the available target types.