Change worldcloud handling from multiple charts to one

The wordclouds are now handled by a chart called wordcloudList that generate a list of wordclouds, I for each word cloud.

The point of this is that it's dirty to instanciate the wordclouds charts for multiple reasons. The most important one is that is you instanciate the wordclouds charts, when chaging cube, you will have to remove the charts and recreate those.

With a chart that is a list, you just remove the dimensions and reaffect new ones.

It also simplifies the code.