ow.ch: Implement a MVS channel type

[nmaguiar]

Implement a channel type using H2 MVStore with options to be persisted in memory or disk, map with a single name or based on a function, optional map housekeeping with a function, compression options, etc.
Then probably some ow.ch.utils functions to provide map names and housekeeping based on date and housekeeping based on number of records. This would be useful for a new output on nattrmon.

[nmaguiar]

Done in be6d258