Moved publishmessage method into separate file.

ie changing names of interfaces and moving structs to other files. Also
gitignore updated to ignore the 'make coverage' outputs.

An error message now gets published if there is an error while
converting the query or there is a database error.

Mainly testing the handlemessage method with different input messages.

Implements the ConvertQuery method and just returns a hardcoded string
value.

Mock producer can now be made. Producer can publish messages. Messages
can be retrieved from the mock broker.

Also changed around some of the naming.

Merge branch 'develop' of git.science.uu.nl:datastrophe/microservices-backbone/query-service into develop