Add GUI warning for DCC-shared avatars

[AndrioCelos]

Currently the GUI allows using a HTTP URL or a local file as an avatar just fine. The problem is that in the vast majority of cases, the user isn't set up to host a DCC session to actually share the file. It may be helpful to show a warning in the GUI that sharing a local file requires some setup, and suggest using a service like Imgur to host the file instead.

[wodim]

How about we remove the option to have avatars sent by DCC entirely?

[swarfega]

Id agree with Wodim, I think DCC could be open to abuse. Best to use self hosting somewhere.

[staticfox]

+1 for removing

[Stanzilla]

+1 for removing

[copywrong]

I had to disable automatic DCC transfers (automatically accept on incoming file) to prevent the downloading of avatars. I wouldn't mind if you removed avatar sharing via DCC.