Default sort criteria filters for member lists

[sooskriszta]

Now that #921 has enabled multiple ways of sorting member lists, we should offer admins the ability to decide the default sort order they want to implement on their sites (as opposed to force sorting all sites by "freshness").

The configuration could take the form of a wp-config filter.

[DJPaul]

We certainly wouldn't want a UI option for this or a constant (which is what I assume you mean by your wp-config.php reference), but we're always happy to add filters to let other plugin developers build these customisations if required.

This needs someone to look at the code and identify what work is required.

[sooskriszta]

Yes, the wp-config.php reference was meant for a constant.

[slaFFik]

Closing in favour of older #2147