The /metering/usage/:app handler repeated the "an app reads only its own
usage" check while the service still let any app read the global bucket.
The service now refuses an app actor anything but its own app, and the
handler only resolves names. Status codes for app actors are unchanged; a
user reading os-global gets their global usage instead of a name-lookup 404.
whoami no longer sets taskbar_items to undefined for app actors, and only
keys with a value count as built, so a listener can't fill one in for an
app. getMonthlyUsage's JSDoc notes allowanceInfo is account-wide.
* fix: scope whoami billing details and monthly usage to the calling app (PUT-2015)
* fix(metering): refuse an app another app's detailed usage (PUT-2015)
Daniel Salazar