OL-Cesium 1.32 release

[Guillaume Beraudo]

Hello,

I am pleased to announce version 1.32 of OL-Cesium, based on OpenLayers 4.4.2 and Cesium 1.38.

This release brings several improvements:
- nested ol.layer.Group synchronization;
- basic cluster source handling;
- dedicated 3D geometry for features;
- contributions to ease implementing Cesium lazy loading and configuration.

As usual, see CHANGES.md for details.

Thank you to all contributors of OpenLayers, Cesium and OL-Cesium.
Especially to first time contributor Jannes Bolling and its sponsor.

Cheers,

Guillaume