Always add custom fields to result of list of fields

Fixes https://github.com/Graylog2/graylog2-web-interface/issues/997
pom helps to be able to build this thing
add YourKit sponsoring notice to README
add yourkit logo to README
Add missing @JsonCreator to CreateOutputRequest#create
Make "streams" optional in CreateOutputRequest
add reading json files from disk

add one stupid test for inputs (which needs more work but illustrates how it could look like)
Add placeholder method for stream testing.
Start tests for StreamRouterEngine.
Merge branch 'master' into stream-speed-improvements-router-engine
Add StreamRouterEngine tests for multiple rules and streams.
Add test for inverted rules.
Refactor tests.