Relax constraints on has-input to allow SO sequence features

[lpalbou]

Following shex errors mentioned in geneontology/geneontology.github.io#269 (comment) and the discussion on shex error reporting: #257

A model was spotted invalid by shex because of an activity has input SO term. SO term don't seem to be handled in shex right now, if we wanted to authorize such pattern, it would have to be added here:

go-shapes/shapes/go-cam-shapes.shex

Line 371 in e05a415

has_input: ( @<ChemicalEntity> OR @<ProteinContainingComplex> ) *;