support a lightweight groovy-friendly createChild on ApplicationBuilder
viz. createChild(Type, flag: value, flag2: val2), as in new WebClusterDatabaseExampleGroovy example;
also:
- resolve HasConfigKey immediately (removing the "config2" map)
- support config keys in the map passed to configure (as well as flags), with many more tests
- fix display name
fix DynamicGroupTest subscription assumption (caught by buildhive) and improve javadoc
Merge pull request #507 from ahgittin/fix/new-entity-model-nicer-groovy

support a lightweight groovy-friendly createChild on ApplicationBuilder