Add support for batch processing by level

[EdwardSafford-NOAA]

Description

Extend the batch processing mechanism to plot data by channels to instead plot by levels. This is needed in order to generate the Ozone and Conventional DA monitoring plots which use level as a coordinate instead of channel.

I'm not sure if/how this might relate to #124 so I've opened it as a separate issue.

Requirements

Given an Ozone time series yaml file, generate plots by level.

Dependencies

None

[EdwardSafford-NOAA]

Closed by #157 .