* Rename reachabilityManager.data to dataForInsertion, and use it only during insertions
* Make reachabilityData an interface
* Fix db serialization of reachability data
* Fix reachabilityDataStore
* Fix all tests
* Cleanup debugging code
* Fix insertToFutureCoveringSet
* Add comments
* Rename to ReachabilityData and MutableReachabilityData