Datadog Java Persistence API Code

added collection mapping. still needs work.

Finished moving to Row. replaced methods that treated a ColumnValueCollection as a full object record, replaced with Row[].

updated object sql generation, prep for collection mappings

preparing for major overhaul to introduce multi-row ClassValues, will change fecking everything

mapping descriptor cleanup, adding type service adapters to allow some mappings to use either a Type or a CompositeType, but haven't cut over to it yet.

folded builders into descriptors. next checkin will see builders removed - for now, they're present but dormant.

Type, CompositeType, annd CompositeMappingService all workin...

finished cache concurrency and cache isolation factory stuff, also put types throughout most column value stuff (a little more to go)

cache overhaul.