Replace yuicompressor with wro4j

[bjagg]

YUI Compressor is outdated and does not support ES6. It needs to be replaced. WRO4J looks like a worthy replacement; although, alternatives should be investigated.

[bjagg]

https://github.com/wro4j/wro4j

[bjagg]

https://github.com/uPortal-Project/resource-server/blob/master/resource-server-core/src/main/java/org/jasig/resource/aggr/ResourcesAggregatorImpl.java