Display an appropriate message when the quota is reached on WebDAV

Prerequisite:

• Install the Quota addon
• Configure the quota on the personal Workspaces to the limit of 2 MB

Steps to Reproduce
1. Connect the Nuxeo using “Map Network Drive…”
2. Login with Administrator
3. Navigate to the Administrator workspace
4. Attempt to copy a file whose size is greater than 3MB to the Administrator workspace which would take the user over its quota.

Actual Result:
When the copy gets to the last part, it fails with "Can't read from the source file or disk".

Expected Result:
Need to notify the user that the Quota is exceeded

Returning a 507 error code is enough to achieve this purpose.