Oops, include the fee in the column list as well

I added it to the parameter list and the VALUES list, but not the
actual column list in the query...
Fix object name of paypal transaction information

In the cronojob the object is trans, not ti (it's ti in the web context)
It appears paypal returns the fee as negative in some APIs...

... and positive in other APIs. Yay for consistency.
Make the ledger report include per-account summaries

This requires rewriting the report as a general SQL query, since
the django ORM is incapable of dealing with window aggregates.

To database people that makes it *more* readable, though :)
Use blank instead of zeroes in report for readability