Create folder modal in file manager does not focus on the text input field

Issue
Context change - When the user activates create folder modal, the focus is not being put in the modal window but is being sent back to the top of the page. Screen reader and keyboard users now have to make their way back to the modal window, only to find out it's impossible to get back in it (and therefore, close it).

Standard Level
WCAG 2 3.2.2 (A) http://www.w3.org/WAI/WCAG20/quickref/#qr-minimize-error-cues

Impact
Critical

Example Link
http://demo.moodle.net/mod/assign/view.php?id=1778&action=editsubmission

Test Steps

1. Login as a student
2. Navigate to a course
3. Click the assignment
4. Click add submissions
5. Click the create folder button in the file picker with a screen reader one
6. Notice the screen reader starts reading at the top of the page.