BrooklynRestApiLauncher rework

* Reworks `BrooklynRestApiLauncher` to make it simpler to launch servers with different configurations of contexts, filters, security providers, etc.
* Fixes interaction between `BrooklynPropertiesSecurityFilter` and `FormMapProvider`. See `BrooklynPropertiesSecurityFilterTest` for test.

Misc comments:
* Null check added to TestEntityImpl to make invocation from effector in `BrooklynPropertiesSecurityFilterTest` fail if FormMapProvider wasn't used.
i'd be inclined to keep this class in order to have the TODO as a reminder we need tests here but no strong feelings