Give mods a way to reset user name, avatar, about text (with logging)

[cellio]

A misleading or vulgar user name or avatar can cause disruption beyond the profile, and an inappropriate "about" text, even with more limited visibility, can still be disruptive if it for example contains dangerous links. We would like moderators to be able to reset these values.

I say "reset", not "edit", because profiles are global and a change that fits on one community might not fit on another. Better to just kick it back to "user#####", default avatar, and blank text than put mods in the position of having to decide on (and defend) specific edits.

Any reset must log the pre-reset values in a place visible to mods. This helps with review and also facilitates recovery if, for example, 90% of a long profile was fine and the mod would like to assist the user in reconstructing it. (Someday I would like revision history for the "about" text, so the user would have it directly, but we don't have that today.)

I am envisioning an entry on the user mod-tools menu called something like "reset profile fields", which leads to a menu where the mod can individually check off name, avatar, and "about" text. Only the checked values would be reset. An annotation would be added starting "reset profile fields:" or similar and recording the original values. (Annotations already record who made them and when, so that's covered.)

[cellio]

@luap42 has related changes in progress, so pinging. (I think you have a "reset everything" option; this request is for more granularity.)

[cellio]

Check this again after #767 merges.