Add automatic or semi-automatic layer picking

[kingjml]

We often talk in terms of stratigraphy or layering in snow science. Identifying these units can be as much of an art, as it is science. Providing quantitative tools to identify the indices or depths of these units within the snow volume is essential for addressing of large volumes of SMP data. Some potential approaches:

• Unsupervised classification
• Supervised classification with field data input
• Wavelet decomposition