Right now toppartitions can only be invoked on one column family at a time.
This change introduces a natural extension to this functionality,
allowing to specify a list of families.
We provide three ways for filtering in the query parameter "name_list":
1. A specific column family to include in the form "ks:cf"
2. A keyspace, telling the server to include all column families in it.
Specified by omitting the cf name, i.e. "ks:"
3. All column families, which is represented by an empty list
The list can include any amount of one or both of the 1. and 2. option.
Fixes#4520Closes#7864