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.
not needed as part of this pull request but two related thoughts while i'm here:
* the realm is likely something we'll want configurable as part of `brooklyn.properties`
* it has been requested we support single-sign-on across multiple brooklyn nodes, that is something we should look at additionally.