Implement array of conditions instead of a single condition for displaying a field

[juanjoarranz]

Currently, the condition property for a field is a single object with its specifications.

It would be more versatile and useful to use an array of condition objects to display the field when all conditions are fulfilled (or put it in another way, when all conditions return true).

If the array of conditions contains a single condition it would work the same way as of today.