Create misfit map for seismic

(Note that heat maps are already used in ert via Std dev tab (enabled for Fields/Surface parameters))

We want two misfit maps next to each other:

one for observations
another for realizations mean response value (or additionally per realization, if realization chooser is already implemented and thus displaying values per one realization is trivial)
X and Y axes of misfit maps are UTM_X (east) and UTM_Y (north) coordinates. Per domain, those are expected to be the same for observations and all realizations.

Map is then divided into colored "cells". It is prefered that size of the cell is small enough that each cell has maximum one response/observation. Each response/observation is then grouped into the cell via their east/north. If more than one response/observation gets into one cell, value of the cell probably should be their mean.
Generally cell color is grey, but color of the cell which has a response/observation value is defined by this value. Some value-to-color scheme should be chosen.

We have two options on how to divide grid into cells:

Option 1 (more complicated, where users need to provide us the grid file): we plot the grid as it is. Each cell in the grid is mapped to some finite pixel size. Grid doesn't have to be right and straight and there could be gaps between the cells in the cube, which users likely appreciate to see as empty space. Each observation/response can be then assigned to the cell (as we can translate east/north coordinates to the cell number).
Option 2 (probably easier): find out via east-north data in all observations what space we need to cover. Arbitrary divide this space into "cells" and assign each response/observation into a cell.

Edit: Users would like to see polygons in the misfit map plot.