Introduce 'indexable' predicate

[Gavrilov-Ivan]

It should be possible to create special predicates for index definitions - they should be applied to specific object (candidate for indexing) and decide if it should be indexed or not.

Testing:

1. Create method providing predicate for indexed entity related to some property value
2. Create entity instances: one should pass predicate check, another - should not.
3. Process indexing queue (automatically or via JMX console)
4. ER: only instance passed predicate check presents in index

[maistrenkoIulia]

verified