Allow customisation of "About" tab items in profile

Following on from discussions with our own users and #357 we would like the ability to customize the profile fields (including custom fields) which appear on the "about" tab.

One idea is to control this via a comma delimited list of fields / custom fields which would determine whether and what order they are shown in on the about tab.

This has implications for the "more" tab where fields could be duplicated, unless a rule is added there to say "if not in about list".

If this work is undertaken it needs to be in a separate branch so as not to delay our next release.

@gjb2048 it would be good to hear your thoughts on the feasibility of this?