Gregor Anzelj authored Jan 08, 2018 and Robert Lyon committed Jan 16, 2018

We achieve this by having a new pieform rule called 'requiredby' where
we can reference another field and when a certain value is set in that
field it makes this field required.

requiredby rule needs an array containing:
- the 'reference', a string of the name of the related field within the same form
- the 'required', an array containing the values of 'reference' element as keys
  and true/1 for value if this element is required.
-- If the reference field returns true/false then required array would
   have either 'true' => 1 or 'false' => 1 depending on what setting
   is needed

behatnotneeded

Change-Id: I9bc5d15b4035d4a11b81b9355a32044c66ee2199