Fix multiple regressions in IOD

Closes #1181 (closed), #1196 (closed) and #1216 (closed)

I finally decided to remove the abstract class. Each angular based IOD method has its own specifications (Gooding needs range guesses, Laplace needs PV coordinates of one observer, Gauss needs the position of 3 observers). Therefore, having an abstract class isn't an easy task here and trying to find "common" signatures can only introduce noise and bad practicies.