Data Hierarchy/Definition universal behavior for get_ts and get_props

[rburghol]

• individual entity types (ts, props, features, vardefs) have the master model of their type, retrievable via method table_def()
• datasource instantiates its tables for props, ts, features, etx. on creation by creating an instance of each entity type and calling table_def()
• each entity that is instantiated instantaites it's own copy of ts and props,l by calling table_def() for those types as well and can therefore leverage tsvalue_search() and propvalue_search() in same was as datasource can.
• in this way the search methods for an individual entity operate identically to those for the datasource and individual entities
• todo: have individual entities like features store a copy of props and tsvalues
• Force_refresh = false, local, or remote to allow persistence of local state. ie, if ts/prop not on an entity, always check the ds local, and check the remote if not on ds local. But if ts/prop is on the entity, only check ds local if firce_refresh = local, and only check remote if force_refresh = remote