check cardinality for guidance_set child elements in schema

[briesenberg07]

See error for repeating recording_method elements:

For many or most child elements of guidance_set, repeating elements should be allowed to enter different guidance for different RTs. Need to fix minOccurs/maxOccurs in schema and need to check against prop_set-to-HTML stylesheets.

[briesenberg07]

@cspayne I assigned you here but let me take a look at the schema first and then we can follow up and see whether changes will work with prop_set-to-HTML stylesheets.