[BeEncounter] appropriate package

[stvb]

Due to technical (compiler) reasons, BeEncounter was moved from core to core-clinical. However, this is not really a clinical core resource, and it becomes difficult to know in which package to find a relevant resource.

Also BeGoal (and BeCarePlan, BeCareTeam) have potentially non-core-clinical uses..

I would suggest to create a new package (e.g. core-structure) to avoid the cyclic dependencies with core, and still keep core-clinical for pure clinical base profiles.

[bdc-ehealth]

@stvb : see proposal in: https://docs.google.com/document/d/1NyDB9YP5KpOC5YW1geTr5WxZ5MTkflzxf6ZjG9cW23I/edit