New function: encrypt image URL

A new function to encrypt a URL is online.
This function can be used to protect images during a survey.

The function can be found in the File Manager

Select the image you uploaded before and press encrypted image url (the image can only been seen within a running survey)

A really long link is generated. This link can then be implemented inside a survey.

If the link to the survey is given to a third party the encrypted picture will not appear on screen.