Alignment fails when first frame has no good sources

[KathleenLabrie]

For alignment, the first frame in the list is used as the reference frame by adjustWCSToReference. If using the sources to do the alignment, then when no good sources are found in that first frame the alignment goes wrong. As possible solution would be to check the second frame and use that one as reference instead if it has "good sources".

It is recognized that the user can simply re-ordered the list. Still, it might be nice to have an automatic fallback.

Suggestion from HD7845.