Add.. modal allows tab focus to go outside the modal

Note: check tab focus means tab through the dialog and make sure the tab key only focusing on elements within the dialog. Navigate to My private files. Create a new folder button. Check tab focus. Select the create button. Within the file manager, right click on the folder. Check tab focus. Click the Add... button in the file picker Tab through the page and make sure it only select the elements within the modal. Select different repository and check for tab focus. click on a file from 'recent files/private files' repository. On select dialog box, check tab focus. Additional Test (optional): Repeat the above steps with screenreader on and make sure the screen reader only read elements within the modal. Note: This patch doesn't apply for the activity chooser. It is only apply to filemanager and filepicker.