Add support to custom HTML page template

[thibaultmeyer]

Hi,

it would be nice to have ability to customize default html view (eg : title -> rename Multipass to something else) or to use a completely different template (like for the email).

Thanks

[ntodd]

Also, while "handle" makes sense as a generic identity attribute, I believe it is confusing for users as it means nothing without further clarification (I have to tell people "handle" means "email"). Considering that the default "handle" is email, maybe the template should at least be configurable.