isRowSelectable does not work with selectableRowsHeader

If you use `isRowSelectable` to limit the number of selectable rows:

```
isRowSelectable: (dataIndex, selectedRows) => {
if (selectedRows.data.length >= selectRowMax &&
selectedRows.data.filter((d) => d.dataIndex === dataIndex).length ===
0) return false;
return true;
```
and you also have `selectableRowsHeader: true`

Any use of the select all header checkbox will surpass the limits set by `isRowSelectable`. Looking at [selectRowUpdate](https://github.com/gregnb/mui-datatables/blob/a879dc482b2450faf7f50220c050e0211bb66e2d/src/MUIDataTable.js#L1597) is there any way for a consumer of this table to override `selectRowUpdate` to support custom behavior like this without completely forking this repo?

Any advice on how to accomplish this would be greatly appreciated!

Thank you

## Expected Behavior
- `isRowSelectable` is honored by the header select-all checkbox
OR
- Using a new config option `selectAllMaximum`, `selectRowUpdate` honor this option for select all.

## Current Behavior
- `isRowSelectable` is bypassed by the header select-all checkbox

Start in src/MUIDataTable.js at the linked selectRowUpdate implementation and trace how the selectableRowsHeader checkbox selects rows. Verify the behavior against the isRowSelectable example and make the header selection honor the stated selection limit or an explicitly chosen configuration behavior.

Written by the indexing model from the issue text.