Implement items.stackInfo

Used to fetch trophy information.
Set is_sdbable to false in items.info

This hides the "Find sellers" tab, which currently does not work as it
requires economy.bestSDBs
Partial players.fullInfo implementation

Does not include player sprite sheets and activity update.
Stub avatar.getHistory

Used in changing outfits, which currently does not work. Returning an
empty history tells the user they have no outfits.
Merge pull request #4 from Whizy/newapis

New/modified methods to reduce the number of error reports