Allow mobile devices and other non-drag-and-drop-enabled devices to upload files.
Checking for drag-and-drop is not enough, must check for file reader too.
Disable drag-and-drop file upload for touch devices.
Merge branch 'master' into file-upload-button

Conflicts:
	app/assets/javascripts/lib/modernizr.js
Merge pull request #383 from alfajango/file-upload-button

Allow mobile devices and other non-drag-and-drop-enabled devices to upload files