I did not want to move those in previous PR to make it easier to review. Now small cleanup time for readability. (:
## Changes
* Merge series goes to `storage/merge.go` leaving `fanout.go` for just fanout code.
* Moved `fanout test` code from weird separate package to storage.
* Unskiped one test: TestFanout_SelectSorted/chunk_querier
* Moved block series set codes responsible for querying blocks to `querier.go` from `compact.go`
Signed-off-by: Bartlomiej Plotka <bwplotka@gmail.com>
