Support visibility expressions on Deletes

Accumulo can specify visibility expressions for delete markers. During compaction the cells covered by the tombstone are determined in part by matching the visibility expression. This is useful for the use case of data set coalescing, where entries from multiple data sets carrying different labels are combined into one common large table. Later, a subset of entries can be conveniently removed using visibility expressions.

Currently doing the same in HBase would only be possible with a custom coprocessor. Otherwise, a Delete will affect all cells covered by the tombstone regardless of any visibility expression scoping. This is correct behavior in that no data spill is possible, but certainly could be surprising, and is only meant to be transitional. We decided not to support visibility expressions on Deletes to control the complexity of the initial implementation.