Multiple property roots support

Right now, Configurator is able to manage only one root. It looks like it is not enough. The current idea is to provide the ability to maintain multiple property roots, which allows other modules to create their own roots as needed.

ex.:

• indexing.query.bufferSize
• persistence.pageSize

NB! There is not any local/cluster root because it looks like local/cluster shouldn't be there at all. Perhaps it should be a storage-specific feature rather than a property path specific.