Properly track min/max timestamps and maxLocalDeletionTimes for range and row tombstones

First problem is that when we have only row or range tombstones in an sstable we dont update the maxLocalDeletionTime for the sstable

Second problem is that if we have a range tombstone in an sstable, minTimestamp will always be Long.MIN_VALUE for flushed sstables due to how we set the default values for the variables