Make it easier for the site's admin to output Members member types list into their profile header

[imath]

Now that we have an Admin UI to create, edit, delete member types, this means we are making the Member Type feature more widely available (not only for advanced users / plugin-theme developers).

As a result, I believe we should make it visible on front-end using, just like the Group Types, the single Members item header. Otherwise, I'm afraid some users could think: "this Member Types Admin UI is useless??".

I'm suggesting the attached patch which replicate what the Group Type feature is doing to list the Group Types of a group into its header, according to the show_in_list property of the type object.

PS: the patch updates the Member Types Admin UI to let the site's admin set the show_in_list property of the member type object.

Here's a screenshot of how it could look like:

[imath]

In 12797:

Introduce a new template tag to list a user's member types

Just like Group Types can be listed into the displayed Group's header thanks to a specific template tag, Member types now have their own template tag bp_member_type_list() to do the same into the displayed user's header.

BP Nouveau is using this tag. Its header templates and styles has been updated to optimize the output of this list.

By default Member Types will not be displayed, their corresponding object will need to have their show_in_list property set to true.

Fixes #8394

[imath]

In 12799:

Member Types: improve the newly introduced bp_member_type_list()

This is a followup to [12797] in order to make it possible to avoid showing the template tag's label.

See #8394