Added Report Model

I've spent a lot of time this week thinking about the best way to
implement the reports, and this is what I came up with.

But, thinking about it now, there is probably a much simpler and less
vague way of storing the data necessary for a report. It would store
(key,value) pairs that would then be read by a controller to create
every report on the fly. Pre-created reports could be cached
server-side as well.