Currently, only some `JobQueue` types are initialized during startup
(as part of `Environment`, or `SSKEnvironment`). Initialization is
required, however, for a `JobQueue` type to restart any latent jobs.
That means that, for example, a durable `SendGiftBadge` job that failed,
and should be reattempted at a later date, will not in fact be restarted
since no `SendGiftBadgeJobQueue` will be initialized at launch.
This change adds `SSKJobQueues` and `SignalMessagingJobQueues` types,
which are intended to be singletons that hold within them a singleton
job queue for each of our `JobQueue` types. These wrappers are added to
`SSKEnvironment` and `Environment` (from SignalMessaging) respectively,
ensuring that all the `JobQueue`s they contain are initialized as part
of environment setup. The wrappers also avoid the need to add a new
property to the (already large) environment types for each new future
`JobQueue`.
This change also updates all existing call sites that accessed a
`JobQueue` from an environment object, to direct that access now through
the wrapper type.
