Add nicknames for pzh users

The commit adds a step in the PZH sign-up process for users to enter a 'nickname'.  This nickname is then used as their account name at this PZH, and for inter-zone certificate exchange.

This replaces email addresses as user identifiers.  The best user ID is now nickname@pzhdomain (e.g., john@pzh.webinos.org )

Note that this PR requires a similar PR at the PZH provider.

Slight modified version of the following issue - http://jira.webinos.org/browse/WP-959
Jira issue: WP-959