The UrlTemplateImageryProvider will be your easiest route, but is not part of the current packaged release of Cesium. It will be part of the 1.11 release, which is scheduled for July 1st. In the mean time, if your schedule does not allow for the delay, you can download the master branch from GitHub and build your own Cesium package. Once the 1.11 release occurs you can then switch back to the Cesium provided releases.