DB country filtering

[geofjamg]

• Do you want to request a feature or report a bug?
  Bug

• What is the current behavior?
  A 'countries' parameters could be provided to the REST queries to filter geo data by country. This filtering is only done at the network level but not in the DB query.

• If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem
  See TODO in the code in GeoDataService.

• What is the expected behavior?
  Country filtering could be done in the Cassandra query to improve overall performances.

• What is the motivation / use case for changing the behavior?
  DB query performance improvement when the DB contains data for several countries.

• Please tell us about your environment:

  • PowSyBl Version: ...
  • OS Version: ...

• Other information (e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. stackoverflow, spectrum, etc)

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