Phase out getReadsForProbe method in DataStore

[s-andrews]

All of the core storage now uses ReadsWithCounts objects to store data so we don't duplicate values and waste memory.

All of the chromosome level sequence retrieval now returns via ReadsWithCounts, and we now have the option to do this for probes too, but we need to convert the logic in the various quantitation methods to use this. If we can do this then remove the original method we can make stuff much more efficient.