Validation websocket updates are big

[tgandrews]

Expected behaviour

We should send only the changes in validation after the update.

Actual behaviour

Currently we send the count of validation errors for all sections and pages in the questionnaire.

Steps to reproduce the behaviour

Cause an update to a questionnaire

Technical information

We the questionnaire validation state before and after the update so we should be able to calculate the difference which would significantly reduce the amount of information we are sending to the client.

This however is a trade off of server side CPU vs client side network and CPU cost. Which might not be worth it until people are editing large surveys.