Intermediate commit: factored the base operations on ObjectOps and started to apply them to RootObject.

Implemented the new interface on the Rados backend.
Fixed several bugs.

The context handle concept is being dropped, with scoped lock objects in place.
The VFS backent store now compiles.

Intermediate commit: started to implement the garbage collection, plus a producer and consumer action.
The Agent class is becomming too complex, so started to split it up between the current agent (living with the application it represents)
and the AgentVisitor, which will look at it from the outside (for the garbage collector).

The intent log exists in the root entry only for the agent register creation. Then the agent register has an agent creation intent log
as well. And finally for all other usages, the agent's intent log shall be used.

This is a working compilation checkpoint. Some intent logs still need to be removed from the schema.

Some legacy utilities from castor were imported alongside, with some adaptations.