Fix autofocus behavior

[wxiaoguang]

The "autofocus" was abused or misbehaved:

1. When users visit a page but they are not going to change a field, then the field shouldn't get "autofocus"
   • the "auth" / "user" page: in most cases, users do not want to change the names
   • see also the GitHub's "settings" page behavior.
2. There shouldn't be duplicate "autofocus" inputs in most cases, only the first one focuses
3. When a panel is shown, the "autofocus" should get focus
   • "add ssh key" panel

This PR fixes all these problems and by the way remove duplicate "isElemHidden" function.

[wxiaoguang]

[silverwind]

I agree we should eliminate most if not all autofocus, it's often distruptive to UX flow. The one on the frontpage is something many users may be used to, so probably keep that.

The only valid use case for autofocus that I see is when opening a modal to autofocus the first input within the modal, but I assume this is best done with some JS instead of the autofocus attribute.

[wxiaoguang]

The only valid use case for autofocus that I see is when opening a modal to autofocus the first input within the modal, but I assume this is best done with some JS instead of the autofocus attribute.

Fomantic UI already does so: