Conditional formatting

## Expected Behavior

I'd like to be able to format cells based on the value in it to produce, for example, colour gradients based on values. This is a popular feature [in Excel](https://support.office.com/en-gb/article/use-conditional-formatting-to-highlight-information-fed60dfa-1d3f-4e13-9ecb-f1951ff89d7f).

## Current Behavior

I've found a couple of ways to do this but none are quite satisfactory and I was wondering if there are any other suggestions.

The simple method is to use a `customBodyRender` and then insert a styled `` with a background colour. The problem with this approach is that it only colours the little box in the middle of the cell which looks a bit rubbish:


The other approach is to use `customRowRender`, which allows full control over everything so that I can restyle the table elements that own the values, but this means I have to reimplement all the row rendering from scratch including all the nice built-in logic I would usually get for selecting rows:


I also wondered whether there was some CSS-based approach but I was unable to come up with one.

(as an aside, I used [Chroma](https://gka.github.io/chroma.js/) to do the colouring and it's really awesome)

## Your Environment

| Tech | Version |
|--------------|---------|
| Material-UI | 4.4.0 |
| MUI-datatables | 2.10.2 |
| React | 16.9.0 |
| browser | |
| etc | |

The issue points to the customBodyRender and customRowRender entry points; start by reading their current table-rendering behavior and related documentation or tests. Done means a supported conditional-formatting path can style the cell area while preserving built-in row-selection behavior, though the exact API is not defined in the report.

Written by the indexing model from the issue text.