WIP for validation of complex properties

[ghost]

(144)

This PR does the following:

1. Abstracts rules around requiredness/validation into a YAML file, loaded by the model so they can be accessed outside of ComplexValidation
2. Adds custom classes on HTML form elements built by the nested attribute input code.
3. Adds custom javascript to add the 'required' flag once a condition is met, and thus toggle the 'green tick' to a cross in the requirements panel on the right.

The code meets the 'required if any' case, and is configured to support the following cases:

1. complex_person ... if anything other than name is populated, make name required
2. complex_organization ... if anything other than organization is populated, make organization required
3. complex_identifier ... if anything other than identifier is populated, make identifier required
4. complex_date ... if anything other than date is populated, make date required
5. complex_rights ... if anything other than rights is populated, make rights required

Where the role is 'operator' the condition is skipped as this is pre-populated in the instrument tab of dataset and we do no want this field to be required by default.

The code meets the 'required if conditional' , and is configured to support the following case:

1. complex_person ... if name is populated, make role required

CAVEAT: I would caution against the over-use of conditional requirements, it makes the form very busy - the javascript has to loop through the form multiple times and I am concerned about performance if it is doing this for mulitiple different conditions. I have added role as an example.

I have observed 'unresponsive' errors in the browser. The needs testing in a more production-like environment where the JS is precompiled.

TODO:

• add tests

[orangewolf]

can I ask why this change + the require almond below?

[ghost]

I seem to recall needing it, but I'll test without.