Fix position angle when using force_beam
Fix position angle when using force_beam

This makes it consistent with the fit to fixed position.

Also, rename "position+errors" to "position+shape", which is less misleading.
Address #4945.

transientskp/tkp,transientskp/tkp,mkuiack/tkp,bartscheers/tkp,bartscheers/tkp,mkuiack/tkp