SearchIO hmmer3-text: Don't overload the hit_list variable with different datatypes

No functional change, just a rename of a variable to make the code less confusing

Signed-off-by: Kai Blin <kai.blin@biotech.uni-tuebingen.de>
SearchIO: Add optionalcascade getter/setter to allow Hit objects without HSPs

Signed-off-by: Kai Blin <kai.blin@biotech.uni-tuebingen.de>
SearchIO hmmer3-text: HSP entries can be empty for valid hits

This should fix bug #3400 and still needs a test

Signed-off-by: Kai Blin <kai.blin@biotech.uni-tuebingen.de>