Animating an expandable row

## Current Behavior

I am using this example posted here https://github.com/gregnb/mui-datatables/issues/214#issuecomment-450537961band it is a bit jarring when the table is expanded without a smooth transition. The new table row just appears.

## Expected Behavior

Is there a way to animate the transition when a table row is being expanded? Or could it be easily implemented?

I have tried adding a transition by overriding styling as stated in the documentation, by using "createMuiTheme" but I have unfortunately not been able to make it work. My code looks like this:

`const getMuiTheme = () =>
createMuiTheme({
MuiTableCell: {
body: {
transition: '0.55s',
},
},
},
});`

I would really appreciate it if anyone can correct me and tell me what I'm doing wrong :)

Thank you for you hard work. I love the tables! 👍

## Your Environment

| Tech | Version |
|--------------|---------|
| Material-UI | |
| MUI-datatables | |
| React | |

Start with the expandable-row example linked from issue #214 and trace the table's row-expansion entry point. Check how the expanded row is inserted and how styling overrides are applied; done means the expansion has a smooth transition and the supported usage is clear.

Written by the indexing model from the issue text.