Merge changes from CLIMATE-259 (RefactorPlots branch) into trunk

The RefactorPlots branch was created (CLIMATE-259) to capture and refactor work done to support multiple-model/multiple-observation comparisons via the OCW webapp ui, as well as to integrate additional plotting capabilities (Taylor diagrams, portrait diagrams, time-series graphs, etc.) into the set of capabilities accessible via the web ui.

While the refactoring process is not 100% complete, enough progress has been made that it makes sense to merge the changes back into the trunk and proceed with the remainder (e.g.: swapping custom calls for their OCW API equivalents as needed, breaking down the current metrics/plotting routine into discrete metrics and plotting calls, etc.). Doing so will allow us to immediately benefit from the ongoing development of the ocw apis and hopefully get more people involved in watching/commenting on the process.