Checkboxes with long labels

#### Bug, feature request, or proposal:
Bug?

#### What is the expected behavior?
Checkboxes with long labels won't word wrap (as it did in earlier versions). (see bottom part of attacjed image)

#### What is the current behavior?
The labels of checkboxes will overflow the containing element. (see top part of attached image) The problem appeared when I upgraded to Angular 5 from 4-something and I pushed up material at the same time. It's possible this behavior was introduced in an earlier version of material than the latest.

#### What are the steps to reproduce?
Just make a checkbox with a long label inside a card or something.

#### What is the use-case or motivation for changing an existing behavior?
I have a checkbox on a login-page with a long text-string about the user agreeing on this and that. When wrapped it's about three lines with the checkbox vertically aligned on the left side.

#### Is there anything else we should know?
I solved it locally by altering _checkbox-theme.scss from line 88:
```
@mixin mat-checkbox-typography($config) {
.mat-checkbox {
font-family: mat-font-family($config);
}
.mat-checkbox-label { // NEW
white-space: initial; // NEW
} // NEW
// TODO(kara): Remove this style when fixing vertical baseline
.mat-checkbox-layout .mat-checkbox-label {
line-height: mat-line-height($config, body-2);
}
}
```

Comienza en _checkbox-theme.scss_ alrededor de la línea 88 y reproduce una casilla de verificación con una etiqueta larga dentro de una tarjeta o un elemento contenedor similar. Comprueba las reglas de tipografía y diseño existentes en relación con el overflow indicado y, después, verifica que las etiquetas largas se ajusten en varias líneas con la casilla de verificación alineada verticalmente a la izquierda.

Escrito por el modelo de indexación a partir del texto del issue.