allow EnergyBand to describe observations that span two regimes

[pdowler]

Some filters span multiple predefined energy regimes (eg HST filters span optical and UV).

[pdowler]

thoughts in no particular order:

• at CADC we chose the band that intersects the largest fraction of the Plane.energy.bounds interval aka "this is mostly UV"... no one ever noted or complained about this
• it would be feasible change to Plane.energy.emBand [0..2] so that there could be 0 (unknown), 1, or 2 band names; in the case of 2 it would be lower and upper and not include additional bands in the middle (e..g UV-to-Infrared rather than UV-and-Optical-and-Infrared)... serialised in the database could use a single column and | separator (like keywords)

So: feasible = yes, useful = ???

allowing a List value would not invalidate existing metaChecksums since the checksum of a single value is the same if it is in a list (a null and an empty list both contribute nothing and a value and a list of 1 value contribute the same bytes to the metaChecksum of the Plane)

[pdowler]

Cardinality: 0..* aka List