Modern browsers were failing to save the avatars configuration form when

Gravatars were set. When hitting Save, the browser was iterating through

all fields and trying to save their states. The file upload field was

empty, and unfocusable due to being hidden, and this caused modern

browsers to bail on the whole save process.
We now use the approach we use in more modern forms in Review Board,

where we ensure that any subform is a <fieldset> that we can manage

via disabled and hidden states. This will prevent the browser from

trying to save anything in it, restoring functionality.

Verified I could save the File Upload form and the Gravatar form

independently, and that the browser only attempted to send fields from

the respective fieldset.
Unit tests pass.