[GridList] Remove named export

[remcohaszing]

GridList is already exported as default. For consistency the named
export has been removed.

As requested in #9833

Breaking change

-import { GridList, GridListTile, GridListTileBar } from 'material-ui/GridList';
+import GridList, { GridListTile, GridListTileBar } from 'material-ui/GridList';

[oliviertassinari]

@remcohaszing Great job. Thank you!

[dupski]

Just a minor thing, but personally I would find it much easier if everything was a named export and there were no default exports. Its not always clear which I should be using. At the top of one of my files I have

import Paper from 'material-ui/Paper';
import IconButton from 'material-ui/IconButton';
import { LinearProgress } from 'material-ui/Progress';
import Table, { TableHead, TableBody, TableRow, TableCell } from 'material-ui/Table';
import Typography from 'material-ui/Typography';

it would be much cleaner like this:

import { Paper } from 'material-ui/Paper';
import { IconButton } from 'material-ui/IconButton';
import { LinearProgress } from 'material-ui/Progress';
import { Table, TableHead, TableBody, TableRow, TableCell } from 'material-ui/Table';
import { Typography } from 'material-ui/Typography';

Just my 2c :)

[mbrookes]

@dupski We plan to address that differently: #9532