Handling of ChannelIndex

[mdenker]

Current BlackrockIO creates a mess with the ChannelIndex, partly because ChannelIndex is somewhat inconsistent. This issue should fix both, the channelindex object, as well as the way its used in the BlackrockIO:

[ ] Differentiate index/channel_indexes/channel_ids/channel_names
[ ] Create meaningful names of ChannelIndex objects in BlackrockIO
[ ] Make sure only those ChannelIndex objects are created which are used.