Various bits

- Create table for sys chan.  You system could be anything, we can't second guess anything.  It could be a hub, or it could be your media centre, or a mobile phone, so instead of using fixed perms as we do for existing things, we use a table similar to config.  c and k are arbitrary, v will usually be an array of other system channel xchans.  If public_perms is set to 1, v is ignored and anyone can access that resource.

- Change create_directory_account to create_sys_channel.  Still unused, and commented out as is untested.

- Add item flags for bugs, and xchan_flags_normal

- Basic achievements module.  Lacking a UI, but works.  Might, potentially, perhaps spark better ideas in others.

- Xref - generate a referral URL with an xchan.  Not yet used.  Eventually, will allow us to do things like forums "introduce a friend get shineys" or traditional marketing.  But more interestingly, allow referral programs between sites - Single User Hub can send a visitor to sign up at SubscriptionsRUs giving everyone has a reason to promote the matrix as well as their own channels.