extend country with continent

Added new entity content
Updated country entity with M2O association to continent entity
Added entity migration
Added data migration
Tested oro:platform:update command
Tested clean install
If you look at countries list, you'll see that they are loaded from two bundles - OroAddressBundle (ISO countries) and OroCRMMagentoBundle (additional counties). Please, split configuration on two to process only countries from current bundle, and add loading to OroCRMMagentoBundle.