Added permission check for drag and drop

Fixes https://github.com/owncloud/core/issues/10846

When dropping files onto a read-only folder, a notification
is now shown instead of attempting to upload.

This for both the drag for upload and drag from inside the file list
cases.

To test:
1) Share a folder with another user and uncheck "can edit"
2) Login as the second user
3) Try uploading files into that read-only folder with drag and drop
4) Try dragging other files from within the file list into that read-only folder
5) You should see an error notification related to permissions instead of "Target was renamed or moved ..."

Please review @th3fallen @icewind1991 @MorrisJobke 

CC @jancborchardt for the extra notification. I tried to reuse the existing text so that it can reuse the translation.