Persistent navdrawer disables input field #13

I noticed that when a pesistent navdrawer is opened, input fields outside of the navdrawer are "disabled".

Actually they are not disabled but you can't focus on them - thus you can use them.

This seems to be linked to the _enforceFocus in nav-drawer.js (line 151) altough I am not sure sure what its meant to do. I think this is inherited from bootstrap modal code.

As a workaround, one can use $(document).off('focusin.md.navdrawer') to avoid this effect. But I think it shouldn't be necessary to do that when using a persistent navdrawer (or other version without backdrop)