* migrate mysql samples to oas 3.0
* update apache2 to use oas3 spec
* migrate graphql samples to use oas3 spec
* move avro script under bin
* update protobuf samples to use openapi3 spec
* add new files
* Add GraphQL express/apollo server generator
* add basic resolvers; adjust parameters/input types
* small adjustments and improvements
* adjust logger config for GraphQL generators
* remove MaxPermSize form bash script as it will be removed from later Java versions; add isNullable utility helper method; Adjust TODOs for graphql implementation
* re-created samples for graphql config and server generators
* re-added templates for graphql config generator
* add graphql-config-petstore bash script
* add isNullable utility method
* fix javadoc issues
* adjust licence headers
* rename Generator to Codegen for GraphQL classes
* renaming, minor enhancement to graphql generator
* add graphql server samples
* add windows batch files, rename directory