Consolidate Normalizer implementations

<!-- markdown --> This change extends the Normalizer with a handful of new configurations. The configuration points supported are: * `hbase.normalizer.split.enabled` Whether to split a region as part of normalization. Default: `true`. * `hbase.normalizer.merge.enabled` Whether to merge a region as part of normalization. Default `true`. * `hbase.normalizer.min.region.count` The minimum number of regions in a table to consider it for merge normalization. Default: 3. * `hbase.normalizer.merge.min_region_age.days` The minimum age for a region to be considered for a merge, in days. Default: 3. * `hbase.normalizer.merge.min_region_size.mb` The minimum size for a region to be considered for a merge, in whole MBs. Default: 1.