small starting fixes

calling child.type on fieldset controller was giving the name of the
  STI child of DynamicFieldsets::Field, now passing class name directly
children page now prints error messages when update fails
'Back' link on fieldset child now links back to parent 'children' page
rearranged a route b/c fieldset/roots was matching fieldset/:id
show only used questions

added a hide_children function that digs through dependencies to see if
  they came up in the form, if not, removes them from show page render
modified fieldset_renderer to use this function when form_type is 'show'
added dependent destroy

tried using allow_destroy specified in accepts_nested_attributes,
  but it was becoming to cumbersome to find and send _destroy key
added dependent destroy instead, to remove dependency tree
  when fieldset child is removed
added instruction field to form js

it will now hide when dependency is not met
  this required modifying js to fetch id and type, which meant
  adding id and type to form partial
also removed InstructionFields from options to choose as a field to
  depend on when editing a child's dependencies