Jacoco plugin doesn't work with java 8
Convert ObjectSchema to use streaming and lambdas
ArraySchema uses streaming where possible
Use more minimal lambda syntax
Convert JsonSchemaProvider to use streams
Convert JsonSchemaProvider to use streams and Optional
Concatenate streams instead of the result list

Stylistic change that feels more "stream-y".
Code cleanup

Replace if null checks with Optionals + map to make
compiling a SimpleTypeSchema more declarative.
Code cleanup