Rename admin user to sympl, secure permissions

Replaces the 'admin' user created by Symbiosis with a user called 'sympl' instead - less chance of a username collision, and if the users home dir is not /srv, it means we can store things like config files there safely.

Things to remember:

• Backup paths will need checking to ensure /backups /home /etc/sympl and /srv are included.
• Ownership of /srv should be set to sympl, and config files should be set to be owned only by sympl.
• • /etc/sympl
• • /var/backups
• • /srv/*/config
• • /srv/*/config/ssl
• • /srv/*/mailboxes
• • /srv/*/public
• • Must run through domains
• Sympl should be in the www-data group, and public (and subdirs) should be owned by www-data, with permissions set 664.
• things like sympl-ssl should be okay with the dir being owned by www-data
• the FTP user should be changed to www-data
• common apps (vim/htop) should be added to sympl-core recommends
• sensible config defaults should be added to sympl-core for the sympl user

Covers #219 (closed) #170 (closed)