* avro-schema generation fix for arrays with ref to enum (or any non primitive type) to include modelPackage prefix
* sample scenario and generated outputs for avro-schema
* create avro-schema dedicated test file
* Default value for the non required fields to null
When a field is not required, the avro schema has no default value.
Has described in an [avro issues](https://issues.apache.org/jira/browse/AVRO-1803), the property default: null must be set.
If we don't do this in the avro file, when we generate java code from generated avro schema, the builder fail if the data isn't set in the avro data class.
* Update generated avro sample
* Expanding CodableHelper with a more customisable dateFormatter and JSON en-/decoder.
* Ran ./bin/swift4-petstore.sh
* Ran ./bin/swift4-petstore-all.sh again after merge from master.
* Ran ./bin/swift4-petstore-all.sh again after building.
* Ran ./bin/swift4-petstore-all.sh again after rebase latest from upstream master.
* sync master, update samples
* Built and ran ./bin/swift4-petstore-all.sh
* Re-adding code which disappeared in rebase from master.
* Fixed test
* [swift] remove old classes
* [AVRO] Fix the package handling for the avro generator (#3987)
Also fix an issue with the outputFolder that wasn't overridable through opts
* Update sample files through avro-petstore.sh
There's an issue with inlined object but it's already present with the previous commit
* Revert the fix on outputFolder (not a bug)
