Changes have now been made that should allow all members and guests to edit their own avatar (which also allows using their own chosen URL for the image). Sorry it took so long to get an answer to this. This new upgraded platform has made many things very difficult that were easy on the old platform. Please check it out and let me know if it works.
Since TN worked as diligently as he did on this matter, I thought I would also update everyone with pictures as to where the button is not located. It is in a different location (for older members) than it previously was located in the Avatar selection window.
Below are two pictures showing you where it is located (just above the pictures) and what the window should look like once you click the link.
Then simply paste the link to your picture in the box and press upload avatar.
Before pressing the link:
After pressing the link:
And that should about cover the personal avatar question.