- Do not carry it over everywhere as parameter, it is a shared
instance anyway and the lifecycle is pretty much the app lifecycle
from the moment we instantiate a map.
- Rename to BackgroundScheduler because it is a Scheduler that will
do tasks in the background, we don't make assumptions if it is a
thread pool or a single thread.
- Most importantly, remove the dependency from `core` on `platform`.
New interface allows it's users to query additional information about
feature that was provided by qRF interface. This is particularly
useful for clustered features.
At the moment, the annotations implementation in the `mapbox-gl-native`
core is creating concrete layer instances apart from `LayerManager/LayerFactory`
code path.
So, annotations must be disabled if the `LayerManager` implementation does
not provide line, fill or symbol layers (those, used by the annotations).
Note: in future, annotations implementation will be moved from the core to the
platform SDK level(see https://github.com/mapbox/mapbox-plugins-android/tree/master/plugin-annotation)
and `LayerManager` won't need to disable it.
Android still calls "reduceMemoryUse" only while handling a low memory event.
iOS, on the other hand, calls "reduceMemoryUse" every time it enters the background.
