Add either a new `permalink` _data descriptor_ (in gaDefinePropertiesForLayer) or a `permalink` property to the options object passed to the ol.layer.Vector constructor. I would personally vote for the 2nd option.

Today we use a mix of _data descriptors_ (`preview`, `background`), _accessor descriptors_ (`invertedOpacity`, `visible`), and OpenLayers properties (`bodId`, `label`). `invertedOpacity` and `visible` need to be accessor descriptors, to work with ng-model. But, to be consistent, we should use the same mechanism for the other properties. I'd suggest that we use OpenLayers properties for `preview`, `background`, `bodId`, `label`, and other properties we may need in the future. We've observed that descriptors are slow in FireFox, and using OpenLayers emits events when OpenLayers properties are changed, which brings flexibility.