mod_rest: Expand mapping of XEP-0045 join stanza The previous 'join' mapping was apparently lost in translation when swithing to datamapper, so might as well map some properties allowing history control. Usually you probably want either zero history or history since the last known time of being joined. Maybe that the former should be the default?

# Introduction

This module sends a [version query][xep0092] to clients when they
connect, and logs the response, allowing statistics of client usage to
be recorded.

Note that since this is per connection, there will be a bias towards
mobile clients on bad connections.

## Example

    info    Running Running Swift version 4.0