Customer Info

This should allow us, the admins, to query information about a customer
without having to dive in and run a couple redis queries and some
database queries before getting the full picture of who we're talking
to.

It also allows the users to request some data about themselves. Balance and
phone number are already visible in other places, but their expiry is currently
not, and people have been asking about it.

Remove BigDecimal.new

It turns out in newer versions of Ruby this isn't cool anymore.
The new way is BigDecimal(value), which is dumb, but whatever...

Customer always has a JID

Factor out CustomerRepo

Using the Repository pattern to encapsulate the fetch and create operations on
the persistence layer for a domain object.  These were not really factories in
the classic sense, but rather "fetch from persisitence layer" methods, and so
they now have a home.