map reprojection but better

[elastufka]

Changes:

• minor bug fixes
• added get_sdo_position() to get SDO trajectory information from drms
• get_solo_position() and get_sdo_position() now return reference coordinates rather than observers. These contain more information that is needed by make_fitswcs_header() to correctly make the output header.
• edited create_header() to only return new header accounting for reprojected cutout size (unnecessary to return both WCS and header)
• edited reproject_map() to work with observer or reference coordinate, and to warn if desired reprojection is likely to take a long time/crash Python by trying to reproject to a very large array

Tests:

• unable to run test in tests/ since stixcore.ephemeris doesn't exist publicly on GitHub
• tested with STIX image -> AIA frame and vice versa using submaps, works as expected