In-place volumes plugin improvements

[tnatt]

There is a need to improve the existing volumetrics plugins. The plotting options are limited, and there is no easy source comparison. Often other tools (e.g. Spotfire) are used to present the data instead.

Desired functionality:

• Today there is two volumetrics plugins in webviz-subsurface, InplaceVolumesOneByOne and InplaceVolumes, it would be good if the new volumetrics plugin could cover functionalities from both.
• Flexible display of volumes - support subplots and different plot types
• Computation of NTG, poro and sw from the data
• Easy comparison of sources (model updates or geo vs eclipse volumes) - e.g. compute diff columns
• QC functionality for fast identification of volume changes and causes (bulk/sw/poro)
• Option to split tornado plots in bulk vs inplace sensitivities

Existing issues related to inplace volumes: #433, #388, #296, #236, #100, #493