REFACTOR to prepare the development of queryContext compound in mongoBackend
ADD queryContext functionality for compound values in mongoBackend
REFACTOR functions generating compound values in queryContext processing at mongoBackend
A few typos fixed
FIX problems raised during code review
Merge branch 'task/mongo_query_compound_values' of github.com:telefonicaid/fiware-orion into task/mongo_query_compound_values
Merge pull request #286 from telefonicaid/task/mongo_query_compound_values

queryContext compound values at mongoBackend