Sitewriter doesn't have sufficient domain rules to read hst:formfieldvalue

When I created a project with 7.8 archetype, there's a domain rule for
'sitewriter' to read/write /formdata/** nodes. The default domain rule
has rules for 'hst:formdata' and 'hst:formdatacontainer' node types.

However, it doesn't include a rule for 'hst:formfieldvalue' node type.
Because of that, the following always fails:

// org/hippoecm/hst/component/support/forms/FormUtils.java (L#97~)

session = getWritableSession();
// – SNIP –
// fetch previously stored form field data (nodes)
if(persistedFormData.hasNodes()){

By default, the sitewriter cannot read hst:formfieldvalue nodes, so
'persistedFormData.hasNodes()' seems always to return false!
By the way, one strange (not so intuitive) thing is that the sitewriter
can create hst:formfieldvalue nodes, but can't read those even without
the extra rule!

So, I think we'd better add one more rule in the default setup for
'hst:formfieldvalue' in either the archetype.