Rewrite of the pipeline control widget

The pipeline control widget now stores its state in the
layer model, where most of the complicated logic has been moved.
The layer model stores additional information internally to
cache things like color and visibility.

One change from previous behavior is that (by default) all layers
will be hidden.  The default behavior can be changed by providing
a query string as the first argument to the constructor.
fixing initialization of layer model in various places
Merge branch 'pipeline-control-cleanup-old' into pipeline-control-cleanup

* pipeline-control-cleanup-old:
  fixing initialization of layer model in various places
  Rewrite of the pipeline control widget

Conflicts:
	web/src/js/app/views/Composite.js
	web/src/js/lib/widgets/PipelineWidget.js
fixed layer model initialization, and construction in the composite views.
hide the histogram tool initially for the composite view, remove debugging print.
Merge pull request #78 from Kitware/update-pipelinewidget-layermodel

Update pipelinewidget layermodel