Replace Configurator et al

[adamretter]

The goal is to replace the Configurator (e.g. org.exist.config.*) with an approach that is less intrusive, leaks less abstractions and is more robust.

Current issues with Configurator:

1. Intrusion into the object itself:
   1. The object must call the Configurator to instantiate itself.
   2. The object must annotate its members correctly.
2. Calling Configurator.configure(this, config); from the Constructor of an object:
   1. Leaks the this from the constructor. See Java Concurrency in Practice: 3.2.1 Safe Construction Practices.
   2. May silently fail. i.e. the Object could not be configured, but these errors/exceptions are silently swallowed by the Configurator, resulting in an unconfigured object; Usually due to a coding bug elsewhere.
3. org.exist.config.Configurator is unfinished:
   1. It contains many //XXX: comments which hide the TODOs.
   2. Error handling is not complete or safe/robust. e.g. the comment: //XXX: must be exception.
4. Does not scale:
   1. The current approach keeps all configured objects in memory. If you have many groups and users this can rather use up a lot of RAM for objects which may never/rarely be accessed.