Fix links in included AuthMethod documentation
Make requests_session app-instance-specific

Different apps can have different User Agent configurations, so they should be able to use those different configurations and not have the last one configured clobber the others.

Also made the killmail handlers use the global session.
Fix payout total for PermissionRequestListings

It was multiplying the payout total based off of (I think) how many permissions were being filtered out. This moves the request filtering into a subquery, and then calculates the payout off of that subquery.

Fixes #58